The big surprise in this election isn't that President Obama is favored to hold on. It's that Senate Majority Leader Harry Reid is. InTrade gives the Democrats a 79.9 percent chance of controlling the 113th Senate. Pollster Nate Silver gives them a 95.3 percent chance of a majority. In both cases, the odds of Democrats keeping the Senate are higher than the odds of Obama winning reelection.

Harry Reid can only hope. (Julie Jacobson - Associated Press)

In June, InTrade gave Democrats less than a 30 percent chance of holding the Senate. That was far below Obama's odds, and it was even below House Minority Leader Nancy Pelosi's odds of retaking the House. The reason was math: Senate Democrats are defending 23 seats to the GOP's 10. That they might pull this one out is, as one Democratic Senator marveled to me recently, "ludicrous." 

But they might. In fact, they probably will. That means that even if Mitt Romney wins, he may not be able to accomplish key goals like repealing the Affordable Care Act.

Blame (or, if you're a Democrat, credit) for this state of affairs goes to the Tea Party. Harry Reid would likely have lost his majority -- and his seat -- in 2010 if the Tea Party hadn't successfully knocked out top-tier challengers in Delaware, Colorado and Nevada and replaced them with more extreme conservatives. Senate Republicans would be much likelier to retake the Senate tonight if Richard Lugar and Sarah Steelman were running rather than Richard Mourdock and Todd Akin.

But it's not just that the Tea Party has been instrumental in helping Senate Democrats hold the majority necessary to protect Obamacare. It was the primary challenge against the late Sen. Arlen Specter that pushed the Pennsylvanian to switch parties, thus providing Democrats with the crucial 60th vote needed to break the Republican filibuster and pass health reform.

This is, in the end, likely to be the ironic legacy of the Tea Party and the tactics it chose: It arose in ferocious opposition to Obama's agenda, but by driving Specter out of the party and pushing pure conservatives over more electable Republican candidates, it gave Senate Democrats the majorities they needed to pass and protect the key accomplishments of Obama's presidency -- and that's before you get into whether the Tea Party's influence in the Republican presidential primaries forced Mitt Romney to the right and gave Obama a crucial edge in a close presidential election.