If Obama’s job-approval ratings remain below 50 percent in 2014, the chances increase that the Senate will be in play. Next year’s electorate could look more like 2010 than 2012 — the consequence of a boom-bust cycle, when the Democrats’ base turns out for Obama, but not for downballot Democrats. The president will be a valuable asset helping the party committees fundraise, but he won’t be welcome in most of the key Senate battlegrounds.

Midterms are rarely favorable to second-term presidents, and this one is unlikely to be an exception. Democrats can’t afford to lose more than five Senate seats (net), and the party is defending seven seats in states that Mitt Romney carried, six of them by double-digit margins. Mobilizing base support on behalf of the president’s pet issues, such as gun control and immigration, will do more harm than good in these conservative strongholds, where Obama is deeply unpopular…

But given Obama’s decidedly liberal positioning to start his second term, the prospect of a midterm GOP wave is very real. The Supreme Court is taking up the hot-button social issues of gay marriage and affirmative action, raising the likelihood of an aggravated conservative base in Republican strongholds. In Southern states, Democrats benefited from high African-American turnout in 2008, which is unlikely to be replicated for the 2014 midterms. And even the best-staffed campaign committee can’t alter forces out of their control. Just ask former DCCC Chairman Chris Van Hollen, who presided over major House gains in 2008 and historic losses two years later.