That track record suggests a Republican-controlled House and Senate wouldn’t completely jump the rails. But even when Boehner wins, he wins ugly. And if the GOP wins the Senate, these fissures will constantly be laid bare in the upper chamber too, preventing the leadership from presenting a consistent and welcoming face to the general electorate, and putting Republican presidential contenders in one awkward position after another.

A titanic budget battle, with the usual mix of unreasonable demands and threat of government shutdown, will be irresistible to the Tea Party once Republicans run all of Congress. But an outside-the-Beltway candidate like Jeb Bush or Chris Christie, inclined to run as someone who can end the federal government’s chronic dysfunction, will be hard-pressed to choose between criticizing Washington or praising the priorities of the Washington Republicans. If another natural disaster hits — especially in a key primary state or swing state — and conservatives again fight against emergency aid, presidential candidates who have a vote in Congress will be forced to choose between the compassion of the average voter and frugality of the debt-obsessed right-winger.

Those are the sorts of headaches that await Republicans if they win the Senate. And what exactly would they gain? Yes, they would be better able to stop Obama from further shaping the judiciary. But so long as they keep the House, they don’t need the Senate to bottle up Obama’s legislative agenda. Nor do they need to win the Senate outright in 2014 to win both the White House and the Senate in 2016. The few benefits do not outweigh the costs stemming from expanded governing responsibilities.