On the face of it, a Republican takeover of the House (or Senate) would seem a good thing—a clear repudiation by the voters of Obama-Pelosi-Reid and the agenda they've proposed. GOPers can claim victory and hold their heads high. But to quote Senator Bill McKay in The Candidate, "What do we do now?"
Republican lawmakers would certainly have their hands full. But on top of dealing with a possible repeal of Obamacare, they would have to worry about the president replicating the Clinton strategy following 1994—a return towards the center, less pressure from the far left. According to Charlie Cook of National Journal, Republicans might be better off if they take away 30 or so seats, but not regain complete control of the House:
Despite all of this disagreement over whether the House will flip, there is pretty much of a consensus in the political community that President Obama's chances of getting reelected will rise if his party loses the House or Senate. (In my book, the latter is quite unlikely.)
There are two arguments supporting the notion that the president might benefit from divided government. First, a GOP-controlled House would provide Obama with a foil. Republicans would have some governing responsibility; Democrats wouldn't "own" Washington and automatically get the blame for everything that does or doesn't happen. A strong case can be made that President Clinton would not have been re-elected in 1996 had Democrats not lost control of Congress in 1994.
The second contention is that losing control of the House would allow (or force) Obama to take a more centrist approach, to replicate the "triangulation" that worked well for Clinton in 1995 and 1996. Positioning himself and his administration as less liberal than congressional Democrats and less conservative than congressional Republicans, Clinton became the moderate honest broker in policy, riding that course to victory over Republican Bob Dole.
In a world where [Senator Robert] Bennett is considered too liberal for Utah Republicans and [Senator Blanche] Lincoln too conservative for Arkansas Democrats, anything that helps presidents move to the middle in time for a general election is likely to boost their chances of winning reelection. Think of the battering that Obama took from many liberals for failing to include a public option in the health care bill. With Republicans in control of the House, will the White House still get that kind of pressure? The short answer: No.
The only problem is, if such a scenario turned out to be true, how do Republicans win but not win overwhelmingly? (This reminds me of some blue humor involving Milton Berle and the punchline, "Just show enough to win.")