The romantic yarn that Barack Obama was born in Kenya, not in the United States, and is therefore an illegitimate POTUS is the core of a still-evolving conspiracy theory that now explodes like a neutron stink bomb splashing on the right wing while leaving the center and left idly smiling and curious.

What is going on with the despondent Republican Party that it hosts loonies called the birthers in its ranks?

The birther episode is not a media story, or even a story about Obama’s unique youth, but another illustration of the slow-motion decomposition of the GOP.

The answer may be that the birther phenomenon is a mutation of a political virus called incoherence. Incoherence is fatal. It killed the Whigs (and led to the creation of the Republicans); it killed the Klan and the American communists. The birther mutation looks to erase what remains of the GOP’s credibility with the electorate, already at an all-time low and still sinking to third- and fourth-party numbers, if there were a third or a fourth party.

In sudden alarm Monday night, 158 House Republicans voted with the Democrats to endorse the self-evident fact that Barack Obama was born in Hawaii. No whipping by the GOP leadership was necessary. The House Republicans understood that birtherism has jumped to a pandemic Phase 6, multiple infections in all states, much too late to stop with a quarantine on the Hill.

Already, a handful of House Republican members show signs of succumbing to the symptoms of brain fever—wagging fingers, dry-mouth stammering—by co-sponsoring a bill to require presidential candidates to submit a birth certificate. The primary patient is California Republican John Campbell, who showed tertiary impatience with his triteness on TV when he proposed, “It doesn’t matter if I have doubts or not, OK?”

August recess means that the Hill Republicans must go home to their districts to face the birtherite pod people, and there will be additional farcical confrontations similar to what the chump moderate Republican Rep. Mike Castle faced recently at a town-hall meeting in Delaware, when birthers flourished their birth certificates at him.

The pandemic is out of control, and those who argue cynically that birtherism is being stoked by the media, or fed by the cunning White House political operation to gain sympathy for a panicky presidency, are not examining the peculiar details of the potency of the illness.

This is not a pandemic that spreads only by the airplane, the Internet, or even by word of mouth, because a single exposure to the central whopper is not usually sufficient. Daily reinfection is needed or the disease goes dormant like algebra. Birtherism has found a durable vector, ubiquitous like insects and slippery like long-tailed mammals, in the institution of talk radio and its cable-TV compadre. The boss vectors just now are the burlesque artist Rush Limbaugh—“Barack Obama has yet to prove he’s a citizen”—and Limbaugh’s parasitic rival of bloviation, faux rueful Lou Dobbs: “I don’t know what the reality is. No one does.”

What is also striking about this mutation is that, as a talking vector, you do not need to endorse the birther template that the president was born of an 18-year-old girl who raced to Mombasa in time to deliver in an unnamed setting. You are just as effective a vector if you deny the birtherite creativity, if you produce the Hawaii documents, if you say the magic words “smear” or “tin-foil.”

White House press secretary Robert Gibbs is a fertile source when he uses the briefing room to evince exasperation: “…this question in many ways continues to astound me.” Cable-TV stars such as the giddy Chris Matthews—“The birthers don’t let the facts get in the way”—and the stern Bill O’Reilly—“ The Factor investigated it and found out that it’s bogus …”—become like Typhoid Marys, spreading an illness to which they claim immunity. Ratings, anyone?

Grimly, the birther episode is not a media story, or even a story about Barack Obama’s unique youth, but rather it is another illustration of the slow-motion decomposition of the GOP. The party, having lost its principles, its confidence, its courage, and then having lost an election, now experiences what it is to lose its mind, too, while it slips into the ash heap with other novelties.

The conduct of the Republicans in Congress since January has been astonishingly frail, as if the party had lost immunities to race-baiters like Limbaugh and Newt Gingrich, to liars like John Ensign and Mark Sanford, to yammerers like Eric Cantor and Michele Bachmann, to the goofily vain like Mitt Romney, Sarah Palin, and Mike Huckabee.

The party has wasted away to the point where opportunistic eruptions like the birthers and much worse are natural sorrows. Republican incoherence didn’t begin with Mombasa. There is logic to the closing down of a great political party that has abandoned its own greatness to cheer on churls. Perhaps what appears terminal cowardice is only venality; perhaps what sounds like a death rattle is only the wrinkled ranting of crones in the Senate; perhaps the polls showing the Republican brand not as well regarded as Drano are just outliers. Perhaps, too, like miscreant HAL 9000, the GOP is warming up to sing, “Daisy, Daisy.”

John Batchelor is radio host of the John Batchelor Show in New York, Washington, D.C., San Francisco, and Los Angeles.