I've been saying for weeks that Democrats hold the political high ground on the tax fight. Sunday, John Boehner all but conceded as much:

“If the only option I have is to vote for some of those tax reductions, I’ll vote for them,” Mr. Boehner said in an interview on “Face the Nation” on CBS, during which the host, Bob Schieffer, pointedly asked whether Republicans would hold the tax breaks for most Americans “hostage” to keep the lower rates for the wealthy.

The key passage here is this: "If the only option I have..." The beauty of being in the majority is that you can control what's on the menu. Middle-class tax cuts are popular. Tax cuts for the rich are extremely unpopular. Republicans managed to pass the latter in 2001 by tying it together with the former, so that anybody opposed to the whole package, even if they favored a middle-class tax cut, could be portrayed as opposed to a middle class tax cut.

Democrats have a much stronger position than Republicans did in 2001. What they want is perfectly in line with what the center of America wants. Forcing Republicans to vote against a popular middle-class tax cut because it doesn't include an unpopular tax cut for the rich is the strongest possible political leverage point. Republicans can't hold up against it, and Boehner demonstrated why.