As the nation prepares to hear the president’s budget address today, many Republicans think Barack Obama is trapped; but it may be that he has Republicans right where he wants them.

So often in his first two years in office, President Obama has acted like a 19th century Whig: he defers to Congress and only enters late in the process to settle differences and reach a compromise. He used this approach first on the stimulus—where he had to scale back Pelosi’s excesses in the final bill—and on health care—where he finally opted for a Massachusetts-style requirement to buy health insurance rather than implement a government-run health care system.

Yet this deference to Congress has been coupled with a law professor’s desire to talk incessantly. As a result, many Americans see a president who at once is overexposed and disengaged. At times he seems like the anti-Roosevelt: he speaks loudly and carries a small stick.

Contrary to conventional wisdom, the budget debate offers him a perfect moment to deliver his presidency from mediocrity and define his place in history. With his recently unveiled reform plan, Paul Ryan may have started debate the about entitlement reform; but Barack Obama could still end up winning it.

A great mystery in history is found in how often great presidents go against type to address a challenge. A leader’s perceived weakness can sometimes be strength.

In 1964, Lyndon Johnson still bore the scars of a career in the Senate spent laboring to obstruct civil rights. Yet he shocked his Southern supporters and transformed the Democratic Party and the country’s political alignment by signing the Civil Rights Act of 1964.

Less than a decade later, Richard Nixon took his anti-communist credentials to Asia where he began to end America’s isolation of China and, in the process, put increasing pressure on the Soviets.

Many historians believe that only Johnson could have passed civil rights just as only Nixon could have opened the door to China. The math adds up better when a president leaves his base and takes on another party’s issue: he keeps most of his voters with him and then coopts enough of his opponents to build a majority.

Such an opportunity now exists for Obama. Having frivolously expanded the annual deficit and the national debt and having created massive new spending programs with health care in his first two years, he could be known in history as the president who expanded the welfare state. Or he could be known as the president who accepted the realities of the budget, reversed course and led the way to reform.

The dilemma facing the president is this: entitlements and interest payments constitute nearly 60 percent of the federal budget. To end deficit spending necessarily means to reform entitlements. Republicans doubt Obama will summon the political courage to do more than offer a few sound bites on the matter. And their doubts seem reasonable. Little exists in the president’s career to suggest that he enjoys confronting his own base. And his base mostly prefers that Social Security and Medicare remain untouched.

Curiously, one sign of the president’s willingness to lead on fiscal policy does exist. It was seen in last year’s health care debate when he insisted that part of the funding for his new health care program would come from cutting Medicare.

Perhaps he reasoned that Republicans would welcome this bit of fiscal restraint. He reasoned wrong. In March 2010, House Republican Leader John Boehner and Senate Republican Leader Mitch McConnell took to the pages of The Wall Street Journal to threaten that “cutting Medicare is not reform.” And Sarah Palin forged her name as a Facebook pundit by introducing “death panels” into the Medicare lexicon. Now, many of the same Republicans who opposed Medicare cuts in 2010 are demanding that the president support Medicare reform in 2011. He should accept their challenge.

After all, even before last year’s debate, Republicans had begun to lose credibility on reducing entitlements. A few years ago a Republican Congress created Medicare Part B, a prescription drug benefit that added even more financial burden to an entitlement already staggering under the weight of insolvency.

Context matters in politics. President Kennedy’s death and the increasing violence in the South led to President Johnson’s embrace of civil rights. And the Sino-Soviet border dispute in 1969 led to President Nixon’s overture to China. Both represented huge gambles; both paid off handsomely.

Similarly, the Republican overreach in opposing Medicare reductions last year combined with the virtually undeniable need for entitlement reform now give Obama a unique measure of credibility at a unique moment in time. The president has been given a second chance; he should seize it if he wants a second term.

Kasey S. Pipes wrote speeches for President Bush and Governor Schwarzenegger, authored “Ike’s Final Battle: The Road to Little Rock and the Challenge of Equality,” and is the Norris Senior Fellow at the Eisenhower Institute of Gettysburg College. He can be reached at info@kaseyspipes.com.