Forget what President Obama and Mitt Romney say they want to do next year. The better question might be: How do they intend to get any of it done? To use a phrase that was popular during the Democratic primary in 2008, what’s their “theory of change”?
One common theory is that the two parties are so far apart that this election, finally, will provide a mandate for the winner and shock the losing side into cooperating. “We’re going to have as stark a contrast as we’ve seen in a very long time between the two candidates,” Obama told donors in Minneapolis. “My hope, my expectation, is that after the election, now that it turns out that the goal of beating Obama doesn’t make much sense because I’m not running again, that we can start getting some cooperation again.”

Rep. Paul Ryan (R-Wis.), speaking at the Reagan library in California, was even more emphatic: “If we make the case effectively and win this November, then we will have the moral authority to enact the kind of fundamental reforms America has not seen since Ronald Reagan’s first year.”
This is conventional wisdom. Elections are arguments about where the country should go next. The candidate who wins the election wins the argument. The opposition party has little choice but to step aside. After all, it’s out of power.
But can you remember the last time it worked that way? The U.S. political system makes winning an election a necessary but very insufficient qualification for governing. The frequent elections in the House and staggered elections in the Senate, the expansion of the filibuster, the influence of the Supreme Court and the polarization of the political parties combine to constrain power. You can win an election and quickly find you lack the support to pass major priorities. Recall President Bill Clinton being stymied on health-care reform, or President George W. Bush’s failed run at Social Security privatization.
If you consider the mechanics of presidential mandates, it’s clear why they don’t amount to much. For one thing, contemporary elections are decided by narrow margins. Had 3.6 percent of the electorate voted the other way in 2008, Sen. John McCain (R-Ariz.) would be president. In 2004, if 1.25 percent of Bush’s voters had switched sides, Sen. John F. Kerry (D-Mass.) would have won. In 2000, well, the winner didn’t even win the popular vote. In 1992 and 1996, Clinton won majorities in the Electoral College, but due to Ross Perot’s popularity, he never won the majority of the popular vote. None of these elections produced the kind of Rooseveltian or Reaganite landslides that cow the opposing party into submission.
Nor is it clear what policies voters have endorsed when they select a president. Some go to the ballot box having read every word of their chosen candidate’s agenda, but most don’t. A swing voter in Ohio might turn against Romney because of his links to Bain Capital without intending to endorse Obama on immigration reform. “In short,” wrote political scientist John Sides in a roundup of academic research on presidential mandates, “we cannot interpret an election outcome as a wholesale endorsement of the winner’s policy proposals (or as a wholesale rejection of the loser’s).”