In a McCain vs. Billary race, the Democrats will sacrifice the most highly desired commodity by the entire electorate, change; the party will be mired in déjà 1990s all over again. Mrs. Clinton’s spiel about being “tested” by her “35 years of experience” won’t fly either. The moment she attempts it, Mr. McCain will run an ad about how he was being tested when those 35 years began, in 1973. It was that spring when he emerged from five-plus years of incarceration at the Hanoi Hilton while Billary was still bivouacked at Yale Law School. And can Mrs. Clinton presume to sell herself as best equipped to be commander in chief “on Day One” when opposing an actual commander and war hero? I don’t think so.

Foreign policy issue No. 1, withdrawal from Iraq, should be a slam-dunk for any Democrat. Even the audience at Thursday’s G.O.P. debate in Boca Raton cheered Ron Paul’s antiwar sentiments. But Mrs. Clinton’s case is undermined by her record. She voted for the war, just as Mr. McCain did, in 2002 and was still defending it in February 2005, when she announced from the Green Zone that much of Iraq was “functioning quite well. ” Only in November 2005 did she express the serious misgivings long pervasive in her own party. When Mr. McCain accuses her of now advocating “surrender” out of political expediency, her flip-flopping will back him up.

Billary can’t even run against the vast right-wing conspiracy if Mr. McCain is the opponent. Rush Limbaugh and Tom DeLay hate Mr. McCain as much as they hate the Clintons. And they hate him for the same reasons Mr. McCain wins over independents and occasional Democrats: his sporadic (and often mild) departures from conservative orthodoxy on immigration and campaign finance reform, torture, tax cuts, climate change and the godliness of Pat Robertson. Since Mr. McCain doesn’t kick reporters like dogs, as the Clintons do, he will no doubt continue to enjoy an advantage, however unfair, with the press pack on the Straight Talk Express.

Even so, Mr. McCain hasn’t yet won a clear majority of Republican voters in any G.O.P. contest. He’s depended on the kindness of independent voters. Tuesday’s Florida primary, which is open exclusively to Republicans, is his crucial test. If he fails, his party remains in chaos and Mitt Romney could still inherit the earth.

That would be a miracle for the Democrats, but they can hardly count on it. If Mr. Obama has not met an unexpected Waterloo in South Carolina  this column went to press before Saturday’s vote  the party needs him to stop whining about the Clintons’ attacks, regain his wit and return to playing offense. Unlike Mrs. Clinton, he would unambiguously represent change in a race with any Republican. If he vanquishes Billary, he’ll have an even stronger argument to take into battle against a warrior like Mr. McCain.

If Mr. Obama doesn’t fight, no one else will. Few national Democratic leaders have the courage to stand up to the Clintons. Even in defeat, Mr. Obama may at least help wake up a party slipping into denial. Any Democrat who seriously thinks that Bill will fade away if Hillary wins the nomination  let alone that the Clintons will escape being fully vetted  is a Democrat who, as the man said, believes in fairy tales.