Republicans’ efforts raise the same perplexing question posed by The Missourian: What drives Tea Party Republicans and their financial backers? What calculation persuades them that repealing the health care law is worth the risk? Indeed, whose interests do they represent?

Nearly 6 in 10 Americans disapprove of trying to stop the law by cutting its financing. Even among those who don’t like the law, less than half want their representatives in Congress to try to make it fail.

It is tempting to discard the Tea Party activists driving the Republican Party as crazy — as some commentators have — motivated by fear and willing to believe that default won’t cause much harm and might even act as a purgative to free the economy of a bloated government.

“They listen to nobody but themselves,” the Harvard political scientist Theda Skocpol told me. “They are convinced of their rectitude and convinced that they alone are qualified to save America from the dire threat of Obama and his polices. They have worked themselves into a dangerous place.”

Their relationship with reality can take peculiar turns. Reflexive opponents of “government,” they can exhibit little sense of what the government actually does.

And yet the argument that half the Republican Party has simply lost its mind has to be an unsatisfactory answer, especially considering the sophistication of some of the deep-pocketed backers of the Tea Party insurgency.

There is a plausible alternative to irrationality. Flawed though it may turn out to be, Obamacare, as the Affordable Care Act is popularly known, could fundamentally change the relationship between working Americans and their government. This could pose an existential threat to the small-government credo that has defined the G.O.P. for four decades.