On February 10th, an eclectic assortment of conservatives streamed into a ballroom in Washington to hear Rick Santorum speak. One woman handed out packages of Government Cluster Fudge (“Cut through the ‘RED TAPE’ and order today!”). Bloggers slung red N.R.A. tote bags over their shoulders. Tea Party supporters arrived, dressed in Colonial regalia and tricorn hats. Dozens of College Republicans took their seats. The occasion was the annual Conservative Political Action Conference, where the fifty-three-year-old Republican Presidential candidate from Pennsylvania was the star attraction. Three days earlier, Santorum’s supporters, mostly evangelical voters, had upended the G.O.P. race by powering his victories in Colorado, Minnesota, and Missouri. Santorum immediately jumped ahead of his rival in the national polls, making him the eleventh Republican leader in the past year.

During the chaotic nominating process in the past year, Republican Presidential polls have been led by eleven different people. Illustration by Costhanzo

In previous years, Santorum likely wouldn’t have survived his dismal showing in New Hampshire, South Carolina, and Florida, three states that held primaries in January. But two developments this year have transformed the race: Romney’s unreliable conservatism, and the ability of rich benefactors to fund Super PACs that can keep campaigns alive. Santorum’s sugar daddy, Foster Friess, a wealthy Wisconsin businessman, introduced the candidate to the CPAC throngs. He began with a joke that elicited knowing guffaws: “A conservative, a liberal, and a moderate walk into a bar. The bartender says, ‘Hi, Mitt.’ ”

Santorum, flanked by his wife and two of their daughters, had the glow of a man who had gone from Party runt to alpha male in a matter of weeks. He had a more serious message than the one Friess had delivered. “As conservatives and Tea Party folks, we are not just wings of the Republican Party,” he said. “We are the Republican Party.”

Santorum’s CPAC declaration has the ring of truth. As Geoffrey Kabaservice writes in “Rule and Ruin: The Downfall of Moderation and the Destruction of the Republican Party, from Eisenhower to the Tea Party,” his careful new history of moderate Republicanism, “The appearance of a Republican Party almost entirely composed of ideological conservatives is a new and historically unprecedented development. It is only in the last decade or so that movement conservatism finally succeeded in silencing, co-opting, repelling, or expelling nearly every competing strain of Republicanism from the party.”

The polls back up Santorum and Kabaservice’s claim. In the past ten years, as self-proclaimed conservatives have increased from sixty-two per cent of the Republican Party to seventy-one per cent, the percentage of Republicans describing themselves as moderates has declined from thirty-one per cent to twenty-three per cent. The number who call themselves “liberal” is now close to the number who describe themselves as Aleut or Eskimo.

The shift to the right has brought new, highly energized voters into the Party, which took over the House and gained six seats in the Senate in 2010. But it has also brought risks. In 2010, the Tea Party helped nominate oddball ideologues in Colorado, Delaware, and Nevada who probably ruined the Party’s opportunity to control the Senate; in 2011, brinkmanship by the new class of House Republicans nearly brought about a government default. This year, conservative forces have pushed the Presidential candidates to extremes. Santorum has talked about “the dangers of contraception” and criticized prenatal testing for women. He has called the President a “snob” for wanting every American to go to college. He said that he “almost threw up” when he read the 1960 speech in which John F. Kennedy declared that “the separation of church and state is absolute.” On immigration, the issue that will define the Republican Party’s relationship with Hispanics, the harsh rhetoric of Romney, Santorum, and Newt Gingrich has alarmed senior Republicans. Rudy Giuliani recently said that the candidates’ statements on some social issues “make the Party look like it isn’t a modern party.” Jeb Bush has lamented that the candidates were “appealing to people’s fears and emotion,” and wondered if he is still a member of the same tribe. “I used to be a conservative,” he said.

Political parties aren’t supposed to act suicidal. For decades, the reigning theory held that politicians, not activists, defined the parties. These politicians were rational people who cared only about winning office. In his 1957 book, “An Economic Theory of Democracy,” Anthony Downs argued that candidates, in their Darwinian struggle to get elected in a two-party system, would cater, inevitably, to what Downs called “the median voter.” Even in a primary campaign, the powerful incentive of having to win over centrists in the general election should keep a candidate’s ideology in check.

But, in the current Republican race, if the so-called median voter were mentioned at a debate, he would surely get booed. A more recent theory about parties better explains the G.O.P. race. In 2008, John Zaller, a political scientist at U.C.L.A., and three co-authors—Marty Cohen, David Karol, and Hans Noel—published an influential book, “The Party Decides,” in which they claim that Downs had it all wrong. The activists, not the candidates, are the crucial players who define and control a party. Interest groups and partisans, like the ones who organize and attend CPAC, care a great deal about policy and ideology, not just about electability, and they decide who gets nominated. Zaller and his colleagues dub them “intense policy demanders,” which, in today’s G.O.P., includes all the familiar factions: religious leaders, gun enthusiasts, business élites, anti-tax activists, foreign-policy hawks. Their mission is to find the most extreme candidate who can win.

The ideal candidate is someone like George W. Bush. Party activists saw him as a conservative ally; swing voters, who, Zaller points out, aren’t sophisticated at detecting a candidate’s ideology, regarded him as a moderate. But sometimes activists don’t have a candidate like that, and they’re willing to risk defeat by backing someone far outside the mainstream. (This strategy can have its own payoff: in 1964, Barry Goldwater lost in a historic landslide, but he changed American politics.) “Parties want to be optimally extreme,” Zaller says. “They are like the frequent air traveller who believes that if he never misses a flight he is getting to the airport too soon.”

This dynamic may help explain the ups and downs of the Republican primaries. Backing Mitt Romney is like showing up four hours early and sitting at Cinnabon; backing Rick Perry would have been like arriving at Newark International in the early evening for a flight that left LaGuardia at noon. And maybe, just maybe, backing Rick Santorum is like getting on the plane right before the doors close.

On a nearly cloudless day in late January, Newt Gingrich stood in front of the P.G.A. Museum of Golf, in Port St. Lucie, Florida, and addressed a modest crowd assembled on a putting green. Gingrich discussed unemployment and housing, then moved on to something closer to his heart. “I want to talk briefly about space,” he said. He gave a short history of the heroism of exploration, mentioning Sir Francis Drake, the sixteenth-century Englishman who circumnavigated the globe; Christa McAuliffe, who was killed in the 1986 Challenger explosion; the American astronaut Buzz Aldrin; and “self-orbital flight.” It was a typical Gingrichian tangent, but his review of America’s journey to the moon and beyond had a point. “Under the élites, the people who oppose me, some in the Democratic Party, some in the Republican,” he said, “under these élites we’ve become the America that couldn’t.”

Soon, he was discussing the Panama Canal, overregulation, and the Second World War. As he linked his improbable candidacy to the defeat of the Nazis, a local man in the rear of the crowd, who said his name was Jim Balsade, began to shout that Gingrich was a “yellowbelly” and a “nut ball,” who was “making crazy statements.”

These days, obnoxious hecklers are a feature of nearly every campaign speech. But a few feet away from Balsade stood three Republican members of the U.S. House of Representatives, who were regaling reporters with descriptions of Gingrich that were only mildly less flattering than Balsade’s. The Romney campaign had sent Mary Bono Mack, who since 1998 has represented the Palm Springs district formerly served by her late husband, Sonny Bono; Connie Mack, a Florida representative and Mary’s husband since 2007; and Charlie Bass, a moderate pro-choice Republican from New Hampshire, to follow Gingrich around Florida and remind reporters what an awful Speaker of the House he had been. A crucial faction of the Republican establishment had descended on Gingrich’s campaign in Florida, with the intent of destroying it.

I asked Representative Bass if Gingrich had any redeeming qualities. “His greatest strength is he’s entertaining,” Bass said. “We just heard a speech in which, for thirty minutes, at least thirty different subjects were covered. He’s a wellspring of information. But this is a Presidential election.” He shook his head as he recounted a House Republican meeting about medical costs in the nineteen-nineties, in which Gingrich abruptly decided that the most important priority for the Party would be the elimination of diabetes. “Another time, we had a whole recess”—the period when members are back in their districts, usually armed with Party talking points—“devoted to ice buckets,” Bass said. “We were going to eliminate buckets of ice delivered to our congressional offices, because that was going to symbolize fiscal discipline. There are bigger issues in America than eliminating buckets of ice.”

As Gingrich’s speech ended, Connie Mack politely excused himself. “I want to see what MC Hammer is saying,” he said, referring to Gingrich’s spokesman, R. C. Hammond, a genial young staffer who made a point of confronting the pro-Romney members of Congress after each Gingrich appearance. The encounters had become a ritual, and they sometimes left Hammond shaking with rage.

Mack approached Hammond, clearly primed for his first debate of the day. Reporters moved into place, unholstering their cell phones and their mini-recorders. “Has Newt answered the question about Freddie Mac yet?” Mack demanded. “Is he going to? Is he a lobbyist?”

As the confrontation escalated, Hammond sputtered something about a lobbyist tied to the Romney campaign who was “peddling influence,” but Mack talked over him: “Peddling is what Newt did when he was paid $1.6 million. He hasn’t answered the question. Why was he hired by the lead lobbyist, why was he hired as a lead lobbyist?” The two sides broke up. Hammond walked over to the Gingrich campaign bus, and the Macks were escorted to their vehicle by a young Romney staffer who was coördinating their travel to the next event. Meanwhile, Clay Walker’s country tune “All American” blasted over the loudspeakers. “I had a best friend with a funny last name and a weird accent,” he sang. “Now he’s an astronaut. We’re all American.”

More than ninety per cent of the ads that Mitt Romney and his allies ran in Florida were negative, though none were as pointed as Gingrich’s final phone campaign, in which he accused Romney of denying kosher meals to Holocaust survivors. In the end, Romney beat Gingrich by fifteen points, and Santorum by thirty-three. But, two weeks later, Santorum was the new leader in the national polls. At CPAC, when I ran into Connie Mack I pointed out that his work in Florida attacking Gingrich seemed to have paid off. “Now we just have to do the same thing to Santorum,” he said.

Fratricidal primary campaigns have become so commonplace that it’s easy to forget that they are a relatively recent phenomenon. For much of the nineteenth and twentieth centuries, a small group of party leaders gathered at the quadrennial Conventions. They usually controlled the delegates, and negotiated over each party’s nominee, based on whatever mixture of electability, ideology, and politics they saw fit. One study of the 1952 election showed that eighty per cent of delegates to the two Conventions were selected by party insiders, with no participation by rank-and-file party members.

Primaries were introduced at the turn of the century by Progressive reformers who wanted to open up the process. But only about a dozen states used them, and they were not always binding when they occurred. Candidates mainly entered them strategically, hoping to show strength to party bosses. The most famous primary victory of the mid-twentieth century probably took place in 1960, when John F. Kennedy, a Catholic, defeated Hubert Humphrey in West Virginia, which was heavily Protestant. “Could you imagine me, having entered no primaries, trying to tell the leaders that being a Catholic was no handicap?” Kennedy said at the time.

The tumultuous Democratic Presidential campaign of 1968 changed the nominating process for both parties. Senator Eugene McCarthy entered and won most of the primaries, which Humphrey, who was the Vice-President at the time, avoided. He intended to win the old-fashioned way: by courting the Party elders.

At the Convention in Chicago, Humphrey won the nomination on the first ballot, even as McCarthy supporters were being beaten by police outside the hall. In an attempt to unite the Party, Humphrey endorsed a commission to reform the nominating system. The commission’s recommendations, which the Democratic Party quickly adopted, required every state party to open up its delegate-selection process to ordinary voters through caucuses or primaries. The changes soon spilled over to the Republican Party as well.

The impact, especially on the Democratic side, was both immediate and short-lived. In 1972, George McGovern seized his party’s nomination by blitzing the primaries and the caucuses with young antiwar voters. In 1976, Jimmy Carter, a little-known one-term governor, won Iowa and then wrapped up the nomination before anyone knew what had happened. When Averell Harriman, the former governor of New York and a longtime Party stalwart, was informed that Carter would likely be his party’s nominee, he replied, “Jimmy Carter? How can that be? I don’t even know Jimmy Carter, and as far as I know none of my friends know him, either.” On the Republican side that year, Ronald Reagan and Gerald Ford engaged in an ugly contest that may have cost Republicans the general election.