In November 2008, just after John McCain was routed by Barack Obama, Jim DeMint addressed a Myrtle Beach conference on the future of the Republican Party. The first-term S.C. senator was there to reassure his audience: Republicans might have lost an election, but conservatism hadn’t lost the country.

His party’s only problem, DeMint promised, was insufficient ideological commitment. Republicans had strayed too far from small-government principle during the Bush era, and then foolishly nominated a moderate like McCain. “Americans do prefer a traditional conservative government,” he told his listeners. But in 2008, between Bush’s deficit spending and McCain’s heterodoxies, “they just did not believe Republicans were going to give it to them.”

This comforting perspective quickly became the official conventional wisdom on the post-Bush right. But DeMint put theory into action and throw his support behind primary candidates who fit his vision of a more authentically conservative Republican Party.

DeMint’s zeal gave his party’s leadership headaches, and his support for no-hopers like Christine O’Donnell helped cost Republicans seats they might have won. But his crusade

succeeded in making Republicans more serious about limited government than the party had ever been under Bush. On spending questions small and large, from earmarks to entitlement reform, the party moved sharply rightward between 2008 and 2012, testing DeMint’s theory that a return to first principles would be enough to win back the White House.

The theory failed the test, and now it’s DeMint rather than Obama who will be leaving office in January. Last Thursday the South Carolinian surprised most of Washington by announcing that he’d be departing the Senate just two years into his second term, to become president of the conservative Heritage Foundation.

Some of DeMint’s admirers quickly portrayed this move as a brilliant way to expand his campaign to remake the Republican Party. But it’s more likely that the move will reduce his public profile, and close a chapter in the history of conservatism.

This chapter was probably a necessary stage for the American right. It’s normal for defeated parties and movements to turn inward for a period of ideological retrenchment before new thinking takes hold.

What’s more, the DeMint worldview wasn’t so much wrong as incomplete. It was important for Republicans to get more serious about entitlements and to shake off their Bush-era blitheness about deficits.

But if DeMint-style retrenchment was necessary for Republicans, it wasn’t anywhere near sufficient. The conservatism of 2011 and 2012 had a lot to say about the long-term liabilities of government but far too little to say about the most immediate anxieties of American citizens, from rising health care costs to stagnating wages to the socioeconomic malaise spreading across the country’s working class. Neither the Reagan legacy nor the current conservative catechism holds the solutions to these problems; they require Republicans to apply their principles more creatively, and think about policy anew.

So it’s fitting, perhaps, that the same week DeMint announced his departure from the Senate, one of the conservatives he fostered gave a speech that tried to do just that. This was Marco Rubio, who used an address at the Jack Kemp Foundation dinner to speak frankly about problems that too many Republicans have ignored these last four years – the “opportunity gap” opening between the well-educated and the rest, the barriers to upward mobility, the struggles of the poor.

The speech didn’t offer the kinds of policy breakthroughs the party ultimately requires. Rubio mixed a few modest forays into fresh territory with a long list of recycled proposals, and he stopped short of the leaps Republicans need to make on taxes, health care and other issues.

But his tone and themes represented a very different response to an electoral drubbing than the kind of retrenchment Republicans embraced four years ago. And as DeMint exits electoral politics stage right, his legacy ultimately depends on whether that difference turns out to be real or superficial – and whether the younger generation he helped catapult to prominence can prove itself more supple, creative and farsighted than its departing patron.