Andrew Sullivan characterizes this post from D.R. Tucker at FrumForum as "pinpointing" the source of Romney's unpopularity with the Tea Party. Tucker's too simplistic. The real point here is that the Tea Party has no point. The Tea Party is an unfocused collective of angry, (mostly) white, (mostly) southern (mostly) Christianists who simply cannot abide a president who does not toe an ideologically pure line, especially one who isn't white. Their anger dominated the GOP after the 2008 election, and those who chose to ride that wave of anger found themselves with enough votes to force out impure incumbents who were willing to make deals with the president and his party. In this election cycle, successive Republican candidates have seen their popularities rise and fall as the Tea Party witnesses that the reality of politics involves compromise in order to govern. They seem just to want the angriest candidate who shows no willingness to make deals. It is classic backlash politics. The trouble is that they don't represent anything anymore except that anger, and anger doesn't have the legs to dominate the national polity for very long.
When a CBS News poll in July revealed that nearly two-thirds of Tea Party supporters wanted the GOP to compromise with the Democrats on the debt-ceiling increase, and a solid 53% wanted the deal to be a combination of tax increases and spending cuts, you know that the idea of a monolithic Tea Party "message" of ideological purity is just pure bullshit.
However, Tucker is right that if Romney gets nominated, the Tea Party brand will be finished as a hallmark of the current GOP. To stay relevant they'd have to split off and form a third party. My hope is that they will do that, because that would mean Democratic dominance of national politics for a long time. Not that I expect brilliance from the Dems -- God knows, I'd like to see a lot of those bums out too -- but it would mean more benefits for the greater good.