If John McCain is elected president, he will have a lot of people to thank. Improbably, first on the list will be the man who didn’t want him in the White House, Rush Limbaugh.

Limbaugh vociferously campaigned against McCain throughout the primary season. He accused the Arizona senator of being a closet liberal and a collaborator with Democratic enemies such as Sens. Russ Feingold and Teddy Kennedy. This caused a lot of glee in Democratic circles. Some optimists even predicted a devastating split in the GOP.

This was a false hope. Limbaugh never had any intention of breaking with his party. When he saw that he couldn’t stop McCain, he swallowed hard and began trying to push McCain to the right. Limbaugh made it clear that he wanted a vice presidential candidate from the Republican wing of the Republican Party.

He got his way with the choice of Alaska Gov. Sarah Palin. Limbaugh now believes, with more than a little justification, that the pick was an effort by McCain to satisfy him and fellow conservatives. And he is indeed satisfied. In an e-mail last week, Limbaugh informed me that, post-Palin, his support for the McCain ticket was “balls to the wall.”

This is a very big deal. A satisfied Limbaugh means an enthusiastic Limbaugh, and an enthusiastic Limbaugh could be the difference in a close race. Between 14 million and 20 million people listen to him every week, by far the largest audience in talk radio. His show energizes the Republican base, but, even more important, it appeals to a great many conservative Democrats and independents of the kind McCain needs to win swing states.

Senior Republican strategists have seen Limbaugh do this before, especially in the 1994 congressional races that gave the House to the GOP for the first time in decades. Limbaugh was so important to that victory that the GOP declared him an honorary member of the Republican House of Representatives’ freshman class.

Fourteen years later, Limbaugh’s influence is greater than ever. No single Republican -- not Karl Rove or Roger Ailes, James Dobson or Sean Hannity -- has his reach and clout. Certainly President Bush doesn’t. Limbaugh is, very simply, the single most influential conservative voice in America.

A lot of Limbaugh’s critics dismiss him as a buffoon or a fanatic. These are people who don’t listen to his show. Limbaugh is not only a brilliant communicator, he is a smart political strategist. Other radio hosts and TV commentators (on both sides) take their talking points from campaign central -- but the people who write the Republican talking points are getting their ideas, often as not, from Limbaugh. Listen to him on a daily basis and you know what Republican candidates are likely to be saying in a day or two.

Early last spring, Limbaugh puzzled over the question of how to campaign against the first black presidential candidate. His decision, as he told me at the time, was to treat Barack Obama with the same contempt and politically incorrect satire he has trained on every Democratic candidate for the last 20 years. He began referring to the Illinois senator as “the messiah,” a nickname that mocks both Obama’s ethereal rhetoric and the adulatory coverage he receives from the “drive-by media.” Limbaugh began playing wicked musical parodies, including “Jeremiah was My Pastor” (to the tune of “Jeremiah was a Bullfrog”), in which an Obama sound-alike warns that linking him to the Rev. Jeremiah A. Wright Jr. could get you labeled a racist.

Limbaugh’s own approach to that charge has been to laugh at it and turn it back on his critics. During the primary season, he appointed his black call screener, Bo Snerdly, as the Official Obama Criticizer, to point out the absurdity of race-based censorship.

Another tactic has been to frame jabs at Obama by quoting from Hillary Rodham Clinton’s primary campaign. On Sept. 19, for example, while discussing race with a caller, Limbaugh asked, rhetorically, “All the racism that has been injected into this campaign’s come from which side?”

Caller: “The Obama camp.”

Limbaugh: “That’s exactly right. Or the Hillary camp, the Democratic Party.”

Last week, the Obama campaign fell into a trap when it tried, in Spanish-language ads, to link McCain to Limbaugh and his supposed disdain for Latinos. The ads sought to make their point with two Limbaugh quotes taken completely out of context. Limbaugh turned this into political jujitsu, branding it, with high drama, as a lie intended to sow ethnic discord.

“Rush emboldens Republicans,” Rove says, and that is certainly true in this campaign. Limbaugh says the things that McCain can’t or won’t say, and pushes both McCain and Palin to ever-tougher rhetoric by raising the bar of acceptable campaign discourse. He also gives permission to his audience to laugh out loud at the Democratic standard-bearer. These are not small gifts to the Republican ticket. Especially not from a man who started out the year as John McCain’s great nemesis.

Zev Chafets most recent book is “A Match Made in Heaven,” about the Christian evangelical movement and American Jews. He is working on a book about Rush Limbaugh.