Political parties have to sell out the movements that support them. First, they exploit the energy, incorporate new activists and ideas, and then find some watered down way to soften the rough edges.

Parties that can’t tame the movements that enliven them, like the Whigs and abolitionism, factionalize, fall apart, and ultimately disappear. Parties that can, support reforms, generate resentment from the base, but win elections and incorporate new movements. Think about the Republicans, beginning with Ronald Reagan, and the Christian Right, to whom he was a bitter disappointment. Think about the Democrats and the nuclear freeze or civil rights. The concessions were always far less than what the activist base demanded. But the parties went on.

Right now, we’re watching the Republican Party in government struggle with defining and coopting the Tea Party–and, at least so far, it’s ugly (as discussed before). The mainstream Republicans, experienced politicians like Speaker John Boehner and Senate Majority Leader Mitch McConnell, share the conventional wisdom among professional economists: failing to raise the debt ceiling, in the best case scenario, means higher interest rates for government securities and for anyone else in the United States who wants to borrow. And they believe it could be much worse.

This is not an odd or idiosyncratic position, even among conservatives. Big business, as represented by the US Chamber of Commerce and the Business Roundtable, shares this view, and has written to the President and every member of Congress asking that, whatever else the government does, it raises the debt ceiling expeditiously. From the Washington Post:

“The business community in large numbers is saying to our leaders in Washington, ‘Do your job,’ ” said Business Roundtable President John Engler, a former Republican governor of Michigan. “Failure to raise the debt ceiling would strike an immediate and serious blow to any economic recovery, and failure to make significant progress on long-term debt reduction will continue the uncertainty which is hampering our investment climate.”

Speaker Boehner has repeated his commitment to responsible governance, and he’s tried to bargain hard with a president who’s quick to make concessions. But he’s had a hard time managing the debt fundamentalists within his party caucus. Senator McConnell has given up trying to cut a deal, and has proposed giving the President complete authority, then campaigning against him.

True to its rhetoric, however, the Tea Party, or at least the organized part of it that has access to media coverage, has been distrustful of both big business and establishment politicians. FreedomWorks, the proto-Tea Party organization that preceded and stoked the movement, insists that the debt ceiling not be raised until Congress effects large budget cuts, enforceable spending caps, and an amendment to the Constitution mandating a balanced budget and making it practically impossible to raise taxes. (Irony alert: Tea Party placards constantly announce fidelity to the Constitution and original intent, even as they plan to change it.)

Tea Party Patriots co-founder JennyBeth Martin sees even the harsh FreedomWorks position as a sell-out. She’s warned Republican members of Congress that the grassroots Tea Party will punish any member who votes for any increase in the debt ceiling at all.

So far, the Tea Party threat, embodied by politicians like Michele Bachmann and the large and committed freshman class in the House, has pulled the Republican Party further to the Right than it’s been in its 150 year life. The question is whether the institutional Republicans or the Tea Party fundamentalists will win this tug of war, or whether the rope connecting them will snap.

Whatever else Speaker Boehner says, he’s professional enough as a politician confronting the debt ceiling to see “218” as the most important number of all those numbers bandied about. That’s the number of votes he needs to find in order to pass the increase in the debt ceiling. If he can’t get 218 Republicans (out of 242), he needs to find Democrats, who will pull the eventual deal back to the center. Whatever politicians say to the cameras these days, behind closed doors they are talking about how (and who) to get to 218.

How this deal works out is supremely important to the Republican coalition. Since the middle-1970s, the Republicans have competed effectively at the national level by joining populist conservative social voters with big business interests. President Obama, to the chagrin of his own base, has made it clear that business is safe with him. The Republican struggle now is to sell the Tea Party out and keep the Tea Partiers in.