Michael Scherer's guess:
In [Bill Galston's] view, the Tea Parties have more in common with Barry Goldwater than H. Ross Perot. They are an intra-party reformist cause, at a time when the nation desperately wants reform. In a midterm cycle, where the choice is between change or the same, it may not matter so much that many of the reforms the Tea Party seeks--like major revisions to entitlements--are not very popular. In other words, the silly campaign rally signs and DNC oppo may matter less than the fact that Tea Partiers are shaking up the Republican Party, which is good for the Republican brand.
That's the optimistic view. I would like to share it. But the social and cultural baggage of the movement - and its support for the unrestrained war machine and visceral recoil from a majority-minority America - seem to point in the other direction. But if they manage to get a GOP House to back real cuts in entitlements and defense, and actually cooperate on some kind of deal with Obama for long-term debt reduction, I'll be more than happy to change my mind. But I see an ideological rigidity that would prevent this. Which would mean more stalemate. Which means more debt.