On the day that he became the all-but-certain Republican nominee, John McCain walked into a cavernous Washington ballroom — to a hail of boos from unhappy members of his own party's base.

Thursday's scene at the Conservative Political Action Conference was nothing short of surreal. Flip Romney, a man dressed in a dolphin suit who first surfaced at last year's event, wandered about aimlessly, out of work after Mitt Romney's surprise withdrawal. Romney himself told the group, with the straightest of faces, that he wasn't quitting because he was losing — he was pulling out for the good of party and country in a time of war.

The resulting cries of anguish suggested that all alleged flipping had long been forgiven — especially in light of the dawning realization that McCain was really going to pull it off.

The CPAC crowd and the Arizona senator are so out of sync that last year, as the race for the nomination got under way, he didn't even bother showing up. This is a group that was on its feet Thursday morning, cheering lustily as Vice President Dick Cheney extolled the virtues of "enhanced interrogation."

To be faced, just a few hours later, with a presumptive nominee who has been one of the loudest voices against the administration's torture policy — well, that felt a little like enhanced interrogation to some of the audience.

It's hard to recall a presidential nominee so at odds with his party's base. "This is the first time in 32 years that anybody's won the Republican nomination without support from conservatives and evangelical voters in the primaries," former Christian Coalition head Ralph Reed said before McCain's appearance at the Omni Shoreham.

Reed may have reason to dislike McCain — the senator's probe into the dealings of lobbyist Jack Abramoff showed him in none too flattering a light — but it is hard to disagree with his analysis.

The implications of these doubts for the general election are unsettling to some Republican strategists. As much as McCain may appeal to independents and swing voters, they argue, he can't win in November without motivating party stalwarts. After all, they don't call it the base for nothing.

"We know John McCain's taken some positions we don't like as conservatives," Oklahoma Sen. Tom Coburn told the group. "John and I have strong disagreements on some issues," added former Virginia senator George Allen.

And these were McCain's assigned warm-up acts, vouching for his bona fides.

If the conference underscored the unusual amount of remedial work that McCain faces within his party, McCain's speech also demonstrated how he plans to go about that task.

"You know, we should do this more often," McCain said with a sheepish smile, and you could see some in the crowd warming — or at least defrosting — as he went on.

McCain packed 17 mentions of "conservative" into the speech: He was "proud to be a conservative" with "conservative convictions." He would run "a campaign based on conservative principles." He would have "a clearly conservative approach to governing." Candidates tend to run to the extremes in the primaries and veer back to the center for the general. McCain doesn't have that luxury yet.

"It is my sincere hope that even if you believe I have occasionally erred in my reasoning as a fellow conservative, you will still allow that I have ... maintained the record of a conservative," he said.

And, most humbly, "I am acutely aware that I cannot prevail in that endeavor ... without the support of dedicated conservatives whose convictions, creativity and energy have been indispensable to the success our party has had over the last quarter-century."

I mean no disrespect by this analogy, but it reminded me of Richard Gere's line in "Pretty Woman," when he takes Julia Roberts to a snooty Beverly Hills boutique: "I think we need some major sucking up."

As much of that as McCain may have left to do, Thursday's speech also sounded the opening gun for the general election campaign: McCain vs. a candidate called, for the time being, "Sen. Clinton and Sen. Obama."

As in, "Sen. Clinton and Sen. Obama want to increase the size of the federal government. I intend to reduce it." Or, "Sen. Clinton and Sen. Obama will raise your taxes. I intend to cut them." They would, McCain warned, appoint liberal judges, yank troops out of Iraq despite "dire threats to our security" and twiddle their thumbs in the face of the threat of a nuclear-armed Iran.

By the end, the booing had diminished. The McCain placards were waving. And McCain had launched his general election campaign while the Democrats battled on, with no end in sight.

Ruth Marcus is a member of The Washington Post's editorial page staff.