If Barack Obama is defeated, the irresistible comparison will be with Jimmy Carter. A one-term president was rejected after pursuing big government programs amid high energy prices and attacks on America in the Middle East.
Actually, that's not entirely fair to Carter. His budget deficits were minuscule next to Obama's, and in response to the Soviet attack on Afghanistan he began the defense buildup that Ronald Reagan accelerated.
Carter supported airline deregulation, which made air travel widely accessible, as well as rail and trucking deregulation, which squeezed billions from the cost of goods and services. He signed a tax bill cutting capital gains rates and establishing 401(k) deferred-tax retirement accounts.
Obama, in contrast, has made big defense cuts and suggested the sequestration process that threatens cuts his defense secretary calls catastrophic. And in the face of voter disapproval, he pushed through Obamacare and has moved toward more regulation on almost all fronts.
In any case, a Romney victory would look like a refutation of the New Deal historians' narrative -- the idea that Democratic presidents increase the size and scope of government, voters ratify that and Republican successors leave it alone till the next Democrat gets in.
If Obama loses, two of the last three Democratic presidents will have been defeated for re-election. The one who won a second term, Bill Clinton, did so only after he declared, after a Republican off-year victory, that the era of big government was over.
What if Obama wins?
Political analysts almost universally agree that any Obama victory will be by a smaller margin in both popular and electoral votes than his 53 to 46 percent win in 2008. He got a higher share of the popular vote than any other Democratic nominee history except Andrew Jackson, Franklin Roosevelt and Lyndon Johnson.
He's pretty much abandoned two states he won last time, Indiana and North Carolina. In polls after the Oct. 3 debate, he has trailed in Florida.
There has only been one president in American history who won a second term by a smaller popular vote percentage and electoral vote margin than four years before. That was Woodrow Wilson, the Democrat elected in a three-way contest against his two predecessors in 1912 and re-elected in 1916 by 49 to 46 percent in popular votes and 277 to 254 in the Electoral College.
If California, which then had only 13 electoral votes, had not gone for Wilson by 3,773 votes, the incumbent would have lost.
In his first term, Wilson had legislative accomplishments more popular than Obama's. A partisan Democratic Congress passed a new antitrust act, created the Federal Trade Commission and the Federal Reserve, lowered trade barriers and imposed an income tax on high earners.
When Americans voted in November 1916, World War I had been raging in Europe for more than two years. Hundreds of thousands were dying in trench warfare, and Wilson ran on the slogan of, "He kept us out of war."
Wilson's second term was wholly unlike his first. In April 1917, he went before Congress and got approval for a declaration of war against Germany. A military draft was instituted, a law passed criminalizing antiwar protests, the railroads were nationalized, and the top income tax rate was raised to 77 percent.
Wilson's idealistic postwar plans were frustrated in the Treaty of Versailles, which was rejected by the Senate. Revolutionaries set off bombs on Wall Street and outside the attorney general's house. Wilson's party lost the 1920 election by a 60 to 34 percent margin.
This history is unlikely to be repeated if Obama is re-elected. But Obama's problem, apparent in the feisty second presidential debate as well as the first, is that voters don't know what he will do -- beyond what he has done so far -- in a second term.
His specific proposals -- 100,000 teachers, infrastructure "investment" -- are retreads. He is less specific on tax policy and budget deficits than Romney.
Presidents who get re-elected usually offer second term agendas. Obama hasn't, especially on the economy. As a re-elected president, he will be as free of constraints, as Wilson was.
Voters must hope that a second Obama term won't be as disastrous as the second Wilson term. Democrats must hope it's not as disastrous for their party.