Mitt Romney took some flak for announcing to thousands of cheering supporters Saturday that Paul Ryan is “the next president of the United States.”

For now, Ryan is merely slated to be the Republican nominee for vice president.

But this is one of those instances where the gaffe is more revealing than the prepared remarks.

With the selection of the House Budget Committee chairman as his ticket mate, Romney has acknowledged that he’s not really hosting this year’s Grand Old Party.

The presumptive presidential nominee has bowed—not a tip of the head here, a full bow—to the party’s conservative establishment and to grassroots right-wingers who demand not electability but absolute purity.

That’s a more significant shift than it might seem. The Romney campaign plan was supposed to follow classic GOP lines: run to the right in the primaries and then, with the nomination secured, pivot at least a little bit toward the center. Even as he battled Newt Gingrich and Rick Santorum in the winter and spring, Romney tried to maintain a measure of ideological maneuverability

No more.

Romney has deferred, fully, to the right.

Until just a few days ago, Ryan was considered an unlikely prospect for the number-two spot on the Republican ticket: too rigid in his budgetary obsessions, too wacky in his enthusiasm for Ayn Rand’s novels and Austrian economics, too enthusiastic about taking apart Social Security, Medicare and Medicaid.

Romney likes Ryan personally—enjoying the frat-boy comaraderie that they displayed while campaigning together before Wisconsin’s April primary—but there was never any doubt that he and his team had their doubts about whether they wanted to let the more dynamic and ideologically pure Ryan define not just the ticket but a potential Romney-Ryan presidency.

It was the right that wanted Ryan on the ticket.

And the right got what it wanted.

In the end, Romney had to bow in order to secure a base that despises President Obama but that never had much taste for the formerly centrist former governor of the only state that backed George McGovern for president in 1972. There was a lingering fear that, as with the Bushes, Romney might go “off message” on them.

Those fears surfaced—“big time,” as Dick Cheney would put it—as the Romney campaign was finishing the vice-presidential selection process.

The first days of August found conservatives entertaining serious doubts about whether Mitt Romney is really one of them. First, one of Romney’s top aides, Andrea Saul, got caught talking up Romneycare (the Massachusetts version of Obamacare) as a cure for what ails the uninsured. Right-wing columnist Ann Coulter responded by calling Saul a “moron,” demanding that Romney fire the spokeswoman.

“Anyone who donates to Mitt Romney, and I mean the big donors, ought to say if Andrea Saul isn’t fired and off the campaign tomorrow, they are not giving another dime, because it is not worth fighting for this man if this is the kind of spokesman he has,” Coulter told Sean Hannity on Fox News Wednesday night. “There’s no point in you doing your show, there’s no point in going to the convention and pushing for this man if he’s employing morons like this.”

Ouch.

But the bigger “ouch” moment came the same day, when it was revealed that the Romney camp had tapped World Bank president Robert Zoellick to head the presumptive Republican presidential nominee’s foreign-policy transition team. Right-wing Republicans dislike Zoellick—a lot—because he is considered a foreign-policy “realist,” with internationalist tendencies. American Enterprise Institute vice president Danielle Pletka described Zoellick as an establishment guy, he’s a trade-first guy. He’s basically a George H.W. Bush old-school Republican.”

On the Republican right, that’s about the same as calling Zoellick an Obama man. Conservative commentators are in full gripe.

What was Mitt to do?

How could he put an end to the debate about whether an until-recently pro-choice “Massachusetts moderate” could really be trusted by the true believers of the contemporary conservative movement?

The pressure on Romney to pick the right-wing favorite for vice president increased as concerns about Romney’s right-wing bona fides rose.

Ryan was endorsed by the editorial pages of the Wall Street Journal and The Weekly Standard. Even Newt Gingrich, who once ridiculed Ryan’s economic policies as “right-wing social engineering,” said Ryan might just be the guy.

Through it all, Ryan gave no ground, sent no moderating signals. The 42-year-old Budget Committee chairman remained the steadily controversial figure he has been over the past several years—thanks, largely (but not entirely), to his advocacy of policies that would lead to the dismantling of Social Security, Medicare and Medicaid. Inside the Romney camp, by all accounts, this fact was duly noted.

But if Romney wanted to get the base in place, he could not opt for a narcoleptic prospect such as former Minnesota Governor Tim Pawlenty or Ohio Senator Rob Portman.

As the presidential candidate admitted, he needed a running mate who would add “something to the political discourse about the direction of the country.”

Translation: Romney needed to confirm his conservative credibility.

Ryan met the ideological litmus tests of the Republican purists. Yes, he is a politician. Yes, he is “DC.” But he is also, at least at this point, the Grand Old Party’s philosopher prince. And his philosophy is not just in sync with the thinking of the Republican right. Ryan embraces and at times defines that thinking.

An ardent social conservative, arguably to the right of Romney on issues such as gay rights and a woman’s right to choose, he was acceptable in ways that other dynamic prospects, such as former Secretary of State Condoleezza Rice, were not. A stalwart on the side of the military-industrial complex who never met a war or a military budget that he didn’t like, and who—despite that nice-guy image—has always been willing to mouth extreme talking points about “foreign” threats, he was for the neocon establishment far more acceptable than “worldly” contenders such as former Ambassador Jon Huntsman or New Jersey Governor Chris Christie. And of course, Ryan was, and is, ever at the ready to promote the fiscal fantasies favored by the hedge fund managers, big bankers and insurance industry interests that fund the vast right-wing infrastructure.

So Ryan passes muster. In the face of the challenges facing Romney at this late stage in a campaign that has had a very bad summer, that has been enough to make him Romney’s pick. As Romney and his team worried about keeping its right flank satisfied, Ryan’s stock rose—rapidly. On Saturday, it moved him to the number-two spot on the 2012 Republican ticket.

Ryan seized the moment, adding star power and rhetorical muscle to the announcement on the USS Wisconsin Saturday morning.

Romney bumbled the introduction.

But Ryan nailed it, earning the loudest applause of the day with a Reaganesque declaration that “America is more than just a place…it’s an idea. It’s the only country founded on an idea. ‘Our rights come from nature and God, not government.’ We promise equal opportunity, not equal outcomes.”

That’s not a new line: it borrows from the Declaration of Independence and the gospels of the Republican right. Romney has tried to deliver it throughout the campaign. The difference is that while Romney has tried, Ryan succeeded. And the crowd went wild.

Indeed, they responded as if Ryan really was “the next president of the United States.”

The problem, of course, is that while Ryan speaks the language of the right, and while the Republican ticket is now fully and firmly committed to run not on Romney’s talking points but on Ryan’s, the Romney-Ryan ticket is going to need a lot more than the purists to win an election that just became a referendum on Ryanism.

Romney will top the ticket. But Ryan is more than a running mate. He is the defining figure for the Republicans from here on out—a development that delighted Democrats who could not quite decide whether the word “radical” or “extreme” better described the ticket. That defining will go way beyond issues of Medicare, Medicaid and Social Security. On every issue that you can imagine, from reproductive rights to environmental protection to labor rights, Ryan stands to the right. Way to the right.

The Ryan selection moves the Grand Old Party harder to the right than at any time since 1964, when the true believers got a nominee, a platform and 39 percent of the vote. America’s more divided now. The Romney-Ryan ticket will run better than Goldwater and Bill Miller did forty-eight years ago, But by bending so far toward the base, Romney has given the Democrats an opportunity to dream not just of winning but of winning bigger than anyone dared imagine forty-eight weeks or even forty-eight days ago.

That’s because they are no longer running against Romney and a ticket mate. They are running against a pairing that, definitionally if not officially, would better be described as the Ryan-Romney ticket.