According to stereotype, the Republican Party runs like a corporation. Lines of authority are clear; leaders are respected and feared. GOP reformers, explained a National Journal article earlier this year, must “come to terms with the hierarchical nature of the party.”

I bet Mitch McConnell chuckles when he hears things like that. Last week, the Senate minority leader came under ferocious conservative attack for allowing a deal that permitted votes on several long-stalled Obama-administration nominees. So at a meeting of Senate Republicans, McConnell said he had not been party to the agreement—a remarkable admission for the man who supposedly leads the Senate GOP. But most remarkable was what happened next: Tennessee’s Bob Corker, one of the senators who hatched the deal, interrupted McConnell’s remarks by yelling “bullshit”.

Stuff like that has been happening a lot. McConnell is so afraid of his party’s right-wing that he’s largely given up trying to cut deals with Democrats. On immigration and gun control, the two biggest legislative issues of 2012, he stood aside and let others do the haggling. As protection against his party’s base, he’s taken to boasting about his friendship with his newly elected Kentucky colleague, and Tea Party favorite, Rand Paul, a man who until recently McConnell clearly loathed.

It’s no better in the House. John Boehner, whom Nancy Pelosi recently dubbed “the weakest speaker in history,” last year tried, and failed, to get House Republicans to back a grand budget compromise with the Obama administration. Then he went to Plan B, which he hatched himself, and they rejected that too. Finally, on January 2 of this year, when he voted for a more modest deal to avert the “fiscal cliff,” he not only failed to bring along most of his caucus. He couldn’t even convince his deputy, House Majority Leader Eric Cantor.

Not that Cantor’s authority is much greater. Since Mitt Romney’s defeat, Cantor has been going around saying the GOP must offer concrete solutions to the problems ordinary families face. But in January, when Cantor pushed a relief bill for communities devastated by Hurricane Sandy, most House Republicans voted no. And in April, when he tried to buttress one of the most popular parts of Obamacare, which makes it easier for people with preexisting health conditions to get coverage, conservative revolt prevented him from even bringing the measure up for a vote.

It’s the same with the Republican National Committee. In March, the party issued a report declaring, “We must embrace and champion comprehensive immigration reform.” Yet most congressional Republicans remain adamantly opposed. Not only don’t these rank-and-file GOP pols fear dissing party leaders, they positively relish it. As Jim VandeHei and Mike Allen recently noted in Politico, “most young conservatives [in Congress] … get more mileage from snubbing their leaders” than supporting them.

Why have Republican leaders become so weak? Partly, it’s the result of not holding the presidency. In the American system, unlike parliamentary ones, opposition parties lack centralized leadership, and thus tend to be fractious. Still, McConnell and Boehner enjoyed a far tighter grip on their rank and file in Obama’s first two years in office, when Republicans stood virtually unanimous against Obama’s fiscal stimulus and health-care overhaul.

What’s changed is the ascendance of the Tea Party. In April, a group of William and Mary political scientists did the most comprehensive survey of Tea Party supporters yet. They found that Tea Partiers have become the foot soldiers of the GOP. Between 2010 and 2013, 73 percent of the movement’s backers were Republicans who attended a political meeting or rally. Those foot soldiers are far more conservative than other Republicans. Indeed, when asked whether they support government regulation of the environment and the existence of the Department of Education, non–Tea Party Republicans were closer to Democrats than to their own party’s activist wing.

Tea Partiers are well aware of this ideological divide. They see the ideological gulf between themselves and the Republican Party as roughly equivalent to the ideological gulf between the Republican Party and the Democrats. That’s a big part of the reason that activists in the Tea Party group Freedom Works are more than twice as likely to rate the GOP “poor” or “well below average” as “outstanding” or “well above average.”

For GOP leaders, this is a massive problem. As Ezra Klein has pointed out, Democrats, independents, and even Republicans say the GOP’s refusal to compromise is its biggest flaw. But the party’s largest faction dislikes compromise. In the William and Mary study, 80 percent of Tea Partiers agreed with the statement “when we feel strongly about political issues, we should not be willing to compromise.” Last year’s RNC report warned that the GOP is “los[ing] the ability to be persuasive with, or welcoming to, those who do not agree with us on every issue.” But Tea Party supporters don’t care. Three-quarters of them told the William and Mary researchers that they’d rather back a Republican candidate they agree with on the issues but trails far behind the likely Democratic nominee than a candidate they agree with less who has a better chance to win.

This makes McConnell's and Boehner’s job virtually impossible. To get anything done, they need to compromise with Democrats. To improve their party’s image, they need to compromise with Democrats. But most Republican members of Congress are more responsive to Tea Party activists—who could defeat them in a primary—than to voters as a whole. And those Tea Party activists oppose compromise, even if doing so hurts the GOP, because they’re not all that invested in the fortunes of the GOP.

If there’s a precedent for this, it’s what happened to Democrats between 1968 and 1972, when the party was taken over by anti-war, civil-rights, and women’s-rights activists. The liberal activists of the late 1960s cared a lot about their causes, and much less about the Democratic Party, which they associated with Lyndon Johnson’s war in Vietnam. Today’s Tea Party activists care a lot about their causes, and much less about the Republican Party, which they associate with the big spending of George W. Bush.

I’m not making a moral comparison. To my mind, the activists who entered the Democratic Party in the late 1960s were heroes. Politically, however, they posed the same dilemma the Tea Party is posing for the GOP today. When your party’s base doesn’t care about the fate of your party, you have a problem. It’s a problem that’s tormenting Mitch McConnell and John Boehner every single day.