McCain Clinches GOP Presidential Nomination

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Candidates React: McCain Accepts Nomination

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"We have a lot of work to do to unite our party and to energize it," said McCain, who will head to Palm Beach, Fla., to begin a swing dominated by intensive fundraising.

Charles Black, his top political fundraiser, said a priority will be to meet with officials at the Republican National Committee to mobilize the national and state parties, which will be critical to the general election.

Now that he has become the de facto head of the GOP, McCain will essentially take over the committee's operations, turning its research, get-out-the-vote efforts and communications into an arm of his campaign.

Looking toward November, McCain has so far aimed much of his criticism at Obama, whose performance leading up to last night's primaries appeared to make him the likely nominee. But the tight races in those Democratic contests made it clear that McCain and the Republicans must be ready to face Clinton, too.

Top McCain strategists believe the ongoing fight between Obama and Clinton will give them time to raise money, develop their strategy and define their candidate to a national audience before a full assault by Democrats. McCain has already begun to paint both potential rivals as dangerous liberals.

"Either candidate, either Senator Clinton or Senator Obama, we will have stark differences. They are liberal Democrats. I am a conservative Republican," he told an audience in Texas.

During the day, McCain talked about the themes he hopes will drive the fall campaign. Mentioning the economy briefly and defending free trade, he quickly moved on to national security, the issue he considers his greatest strength against the eventual Democratic nominee.

Three times, he referred to "transcendent radical Islamic extremism."

But in his speech last night, he also sought to reach out, thanking "independent-thinking Democrats" and pledging a campaign that does not descend into "an uncivil brawl over the spoils of power."

"The contest begins tonight," he said, promising to seek "a government that is as capable, wise, brave and decent as the great people we serve."

Slevin reported from the McCain campaign in Texas.