Under what conditions can the President exercise policy leadership?

Article II of the US constitution gives the President the power to "recommend to their [Congress'] Consideration such Measures as he shall judge necessary and expedient." However, it is only since Roosevelt came to power during the Depression that the presidency has become the provider, promoter, and manager of the legislative agenda. The disastrous economic situation that faced Roosevelt when he took office, combined with his string of proposals to improve the situation, resulted in Congress eagerly passing vast tracts of legislation initiated by Roosevelt. This First Hundred Days marked the end of the Congressional prerogative on legislation-setting, and the source of most legislation now comes from the executive.
Yet the setting of the legislative agenda is only one function of the President; he (or she) must provide the country with a vision or purpose as well. The structure of the political system in the US, including the electoral system, both helps and hinders the fulfilment of these functions. The fact that the President campaigns in a nation-wide constituency and essentially holds all executive power individually (the only branch of government where power is exercised individually and not collectively) work in his favour when working towards the White House. However, once elected, the means with which to set about accomplishing the grand objectives are vastly more limited. This is due to the legislative labyrinth of Congress that must be negotiated (quite literally, as it happens) carefully if the executive is to see any of his legislation pass into law, and the massive bureaucracy which the President heads. For these reasons, what can be termed "effective" Presidential leadership has become a rare commodity, and much of the job that the President carries out is dependent on his skill as a negotiator and his ability to cajole, persuade, threaten, or bludgeon his allies and opponents into accepting his will (or bill).
It would seem that the most beneficial conditions to exercising policy leadership would be found where the party the President is from has a majority in both houses of Congress. However, this is a situation that rarely arises; there have been few occasions in the post-war period when the President has had the luxury of theoretically being in control of the legislature. The most recent occurrence of this was during the 103rd Congress, when Bill Clinton found himself presenting legislation to a Democrat-controlled Congress.
I used the word "theoretically" above because, in practice, there is no obvious advantage to having one's own party dominating the Congress; there is a wide divergence between a party's legislative side and its presidential one. The fragmented nature of Congress renders the building of a coalition both necessary and extremely difficult. There are a wide range of views on any one issue within one party, which means that there will be dissenters who will not support the legislation the President is proposing. On the other hand, and somewhat ironically, the President may find himself being supported by Congressmen from the opposition party; indeed, he may be relying on them to carry his bill through.
In the absence of assured political support, what are the other resources that the President can use to promote passage of his legislation?
The President can use the public support he will have in his honeymoon period immediately after election to form the basis of a flurry of legislative activity. It is unsurprising that most legislation is introduced in this period, as Congress is unlikely to provide as much opposition to a popular President as one who is facing a mid-term crisis in the approval ratings. Congressmen have their own re-election in mind, and blocking a new President's legislation may be interpreted as obstructionism, something their prospective opponent two years down the line would surely drag out of the closet at the mid-terms.
Secondly, the President can make direct appeal to the public by the use of the media. Television broadcasts have become commonplace in explaining to the public major policy, especially in emergency situations, e.g. Reagan went on television to explain the US actions in bombing Libya in 1986 and invading Grenada. However, it is also possible that this may backfire, as was the case with Nixon's televised denials of a White House cover-up regarding the Watergate affair.
The President has at his disposal a personal staff, unelected and directly accountable to him, of around 2000 people, of which 500 work in the White House as his aides. These form the Executive Office of the President (EOP), which was established by Congress in 1939 to help the President. The growth in size of the Executive Office has prompted charges that the President is now effectively shielded from public opinion and political reality. Essentially the role of the EOP is to help the President manage and co-ordinate his legislative agenda; in effect, 2000 Peter Mandelsons trying to co-ordinate different policies into one coherent political agenda. The President even has as part of the EOP the Office of Management and Budget (OMB), which essentially controls the budget, and is somewhat analogous to the Treasury. The power of the OMB is such that in 1975 Congress voted to make the appointment of the director and assistant-director subject to Senate approval.
The 500 aides who work in the White House are the President's most trusted advisors, and none are subject to congressional approval. The growth in this section of the EOP, combined with the failure of the system of checks and balances demonstrated by Watergate, where Nixon was reliant on his advisors to the extent that he was unaware of public opinion, and the Iran/Contra fiasco, where members of President Reagan's White House staff diverted proceeds from a covert weapons-for-hostages agreement with Iran to the Nicaraguan "Contra" rebels fighting the Sandinistan regime, has lead to worries over the lack of accountability, and calls for the downsizing of the Presidential staff who, opponents day, have too much of a free hand to pursue their own agenda without fear of being called to account. Nonetheless, the EOP is a powerful tool that the President is able to use to advance his political agenda, providing he is able to prevent its subversion by those within it, or he does not misuse it, as in the case of Watergate.
The President is also able to make appointments to several different bodies, the most obvious and important of which is his own cabinet. Many cabinet officials are not politicians, but are prominent figures from the industrial, commercial, or academic spheres, who return to their jobs after four years in their post. Others, however, may be seasoned political veterans; state governors or senior civil servants. The posts of Secretary of State and Treasury are usually awarded to those with substantial political knowledge and experience, given the importance of these two departments.
The President can hope to accomplish five things by carefully appointing cabinet officers. The first is to reward important supporters with a prestigious role in the new administration, e.g. Bush appointed James Baker Secretary of State. Secondly, they can attempt to bring in former opponents to try and build an obvious coalition. Thirdly, appointing Congressmen can help foster links with the legislature (although Congressmen, if they accept, must resign before taking up their post as no-one can serve in the executive and legislative branches simultaneously). Clinton did this by giving the role of Secretary of Defense to Les Aspin. Fourthly, there is the obvious politically correct element of appointing women or those from racial minorities. Clinton used this widely: Madeleine Albright was the first female US Ambassador to the UN and Secretary of State; Janet Reno is the Attorney-General (who is proving highly adept at resisting Republican calls into a full investigation of campaign financing), and Ron Brown was one of a number of cabinet members from the black or Hispanic communities (Brown was Secretary of Commerce until he was killed in suspicious circumstances in a plane crash in Bosnia in 1996; allegations of bribery, foul play and cover-ups continue). Finally, a President can appoint those that he most trusts to the cabinet, as John Kennedy did by appointing his brother Robert to the position of Attorney-General.
Whilst an important device for public relations and politicking, the Cabinet carries little political weight, and various Presidents have treated it in different ways according to their view of its importance; Kennedy virtually ignored, whereas Eisenhower found it useful; Reagan was alleged to have forgotten the name of one of the quieter members of his cabinet.
In a similar way, the President has the power to appoint judges to the bench of the Supreme Court and other, lower Federal courts, and ambassadors. By making use of these powers of appointment, he could hope to ensure a sympathetic Court that would not be inclined to overturn the President's legislation, and can even threaten political opponents with the prospect of an appointment as Ambassador to Lesotho or Burkino Faso. All such appointments such as these are subject to Senate confirmation, so the ability to threaten is not as potent as at first sight.
However, the President does hold another key ability to threaten those who oppose him: he has the power to veto any piece of legislation Congress sends to him. A vetoed bill can be overturned by a two-thirds vote of both houses, but it is almost impossible to achieve this, so a veto ordinarily signals the death of a bill. Bush in particular used this power widely; by the end of his third year in office, he had vetoed 24 major pieces of legislation. The introduction of the "line-item veto" may result in the reduction of the use of the veto, since the President may remove certain clauses and paragraphs that are not to his liking before approving a bill; formerly, he would have had to reject the entire bill. This may also help to prevent "pork-barrelling," a term that refers to opportunistic congressmen inserting clauses into legislation awarding their states federal spending, which are sometimes barely relevant to the bill, but which the congressman in question can be sure of receiving as it is likely that the President will sign the bill, as he is in favour of the major component of it.
All of the above mentioned measures are at the President's disposal for exercising policy leadership, but many are reliant on the ability and skill of the President to utilise them effectively. This depends on the character and personality of the President. In negotiating with Congress, the skill of the President in assessing and exploiting situations in his favour can make the difference between a bill passing and failing. Each President can generally be summed up in a couple of words by the electorate after their time in office, and it is usually the public opinion as opposed to any legislative achievements that people remember.
Perhaps the best exponent of the art of co-operating with Congress was demonstrated by Lyndon Johnson, himself a former Senate majority leader. This experience proved invaluable in his relationship with the legislature. Firstly, he was interested in Congress, and said in his time in the Senate that he "wanted the bills to become law." He found himself in a position of strength following the assassination of his predecessor, and was able to capitalise on the foundation-laying work of the Eisenhower and Kennedy years in completing a program of social policies. Although these conditions were to a large extent not of his own making, he nevertheless had the foresight to use them effectively in promoting his own legislative agenda. He also acted quickly in order to push legislation when his popularity has highest; he recognised that his influence would decline as his term went on. On the other hand, he was also persistent in the continued support of his own legislation and in his communications with the Congress. He established means whereby he could engage in two-way contact with the Congress, and conversely would be contactable, and worked closely with the party leaders in the House and Senate. Such approaches to the problem of how to pursue a legislative agenda resulted in Johnson passing major pieces of Civil Rights legislation and pursuing his Great Society. However, the frustrations of the Vietnam war were to haunt him, as he seemed incapable of applying the above principles to foreign policy.
These then are the instruments a President has with which to pursue policy leadership. In the period following a President's departure from office, lasting opinions are formed as to their success or failure in this area. In recent years there have been a succession of perceived failures, e.g. Johnson was undone by the Vietnam war (which, if you believe the conspiracy theories, he helped to instigate by colluding with the CIA and military-industrial bloc in the assassination of Kennedy), and Nixon by Watergate; Ford is seen as being little more than a caretaker before the indecisive and inept Carter; Reagan's successes will be tarnished by Iran-Contra; similarly Bush's Gulf triumph could not prevent a humiliation in the election after the onset of recession, and Clinton will soon be exposed as a lying, cheating, corrupt, drug-running, promiscuous, mass-murdering fraudster. Perhaps this sorry roll call of less-than-acceptable role models is simply a reflection of the lottery-like nature of the electoral system, which results in the wrong people getting into the White House. If this is the case, perhaps it is just as well that they do not have more latitude to act as they wish.