Foreign policy tells a similar story. Obama made some initial attempts to distinguish himself from his predecessor -- for example, he issued an executive order banning torture on his first day in office. But for the most part Obama has continued the policies of the George W. Bush Administration, effectively blunting any charges that he would be weak on terrorism. Indeed, in some respects Obama has gone further than Bush in promoting presidential power. He staged a brief war against Libya without congressional authorization. And he asserts the right to use unmanned drones to target and assassinate suspected terrorists around the world -- even if they are American citizens.

Finally, the comparative strength of the two parties' electoral coalitions suggests that we have not yet witnessed the birth of a new political regime. Like Clinton, Obama was seriously rebuffed in his first midterm election, with Democrats losing control of the House. Although long-term demographic shifts favor the Democrats, the Republican regional base in the South and Mountain West is still quite strong. In fact, opposition to Obama is so overwhelming in these areas that Obama might win the Electoral College by squeaking by in a number of battleground states but still lose the national popular vote. Incumbent presidents often increase their margin of victory in winning a second term, but that is not likely to happen in 2012. If Obama wins reelection, it will probably be by a narrow margin, and not by a landslide.

All these indications suggest that Obama, like Clinton, is a preemptive president. If so, then it will probably take a third Democratic presidency to finally end the age of Reagan. By way of comparison, it took three Republican presidents -- Eisenhower, Nixon, and Reagan -- to overcome the New Deal regime, and it took three Democrats -- Cleveland, Wilson, and FDR -- to break the Republican Party's long period of dominance after the Civil War.

Yet the question is not completely settled. Andrew Jackson, for example, did not really become a transformative president until after his reelection in 1832. In his second term, however, Jackson won a long struggle to dismantle the Bank of the United States, shifting politics in his party's favor for a generation.

Jackson's example suggests that a reconstructive Obama presidency, although unlikely, is still possible. Surely Obama has a remarkable record of accomplishments. The Affordable Care Act is the most important piece of domestic legislation since the 1960s. Of course, if Romney wins, the Republicans will probably dismantle most of Obama's reforms, including health-care reform. Obama needs a second term to secure his achievements.

One Shot at Greatness

If Obama does win reelection, he has one shot at truly remaking American politics. He has an ace in the hole, if he plays it correctly. Ironically, it comes from his presidency's darkest days -- the debt ceiling crisis of 2011.

It will not be easy. But if Obama can hold tough until January, he can strike a deal on entitlements, defense, and taxes that will favor Democratic priorities for a long time.

Because of the deal that ended the debt ceiling crisis, large cuts in defense and social programs will take effect at the beginning of 2013. That is also when the Bush tax cuts expire and the country returns to Clinton-era tax rates. But once that occurs, the baseline for political bargaining between the two parties will be totally different than it has been for the past 12 years. Without lifting a finger, the Democrats will have made the tax code more progressive and achieved major cuts in defense expenditures. And America will be well on the way to solving its deficit problems, as trillions of dollars of new revenues will come pouring in over the next two decades.