WASHINGTON — Three years before he ran for president in 2008, a newly slim Mike Huckabee peddled a book with a title that doubled as a lecture: “Quit Digging Your Grave With a Knife and Fork.” Now, as he considers a second White House run, he has written another book with a decidedly different but equally direct title: “God, Guns, Grits and Gravy.”

Mr. Huckabee’s earlier effort delivered a “12-step program to end bad habits and begin a healthy lifestyle,” as the subtitle had it. It is almost unthinkable that an aspiring Republican presidential candidate would do the same today, given conservatives’ strenuous opposition to Michelle Obama’s healthy eating and exercise campaign.

In its own vivid way, Mr. Huckabee’s march from author of a self-help and clean-living guide to cheerleader of artery-clogging calories and conservative traditionalism highlights the Republican shift during the Obama era.

The party is different in tone and substance, moving toward a stricter, limited-government brand of conservatism in response to President Obama’s liberalism, a change that has generational and ideological dimensions.

Now, deviations from orthodoxy on education, health care, immigration and the environment that some Republicans flirted with or embraced during George W. Bush’s presidency are as out of vogue on the right as flip phones.

It is fitting, then, that the first potential Republican candidates to step out prominently in the new year are Mr. Huckabee, a former Arkansas governor, and Jeb Bush, a former Florida governor.

On the surface they are as different as Ouachita Baptist University, Mr. Huckabee’s alma mater, and Phillips Academy in Andover, Mass., Mr. Bush’s prep school. But they share traits: Each left office in 2007, neither has directly engaged in the party’s fights against Mr. Obama, and if they run, both will be challenged in the primaries on positions they took in a different political era.

The 2016 Republican primaries are shaping up as more complex than formulaic clashes between a center-right, establishment candidate and a handful of hard-line challengers. There are also likely to be fault lines of both age and political sensibility.

Figures like Mr. Huckabee and Mr. Bush, who rose to prominence in that earlier era, are likely to face off with men like Senators Rand Paul of Kentucky and Ted Cruz of Texas, whose vigorous opposition to Mr. Obama has been a central organizing principle of Republican politics.

“This is a cycle in which a younger generation of politicians are coming into the race with a view that small-government conservatism is the ideal and who feel no imperative to bend over backward to show that they are compassionate to people,” said Ben Domenech, a conservative who writes a daily newsletter popular on the right.

Mr. Bush and Mr. Huckabee have each taken positions that are intended to broaden the party’s appeal but that will inflame the Republicans’ more doctrinaire conservatives.

Both backed the Common Core education standards, now detested among many activists because they are seen as opening the door to more federal control. Both have taken a comparatively temperate approach on immigration. Mr. Bush has opposed offshore drilling, and Mr. Huckabee, in the 2008 primary, stated his support for a cap-and-trade program to reduce carbon emissions. Mr. Huckabee has also battled for years with the fiscally conservative Club for Growth because he increased spending and some taxes when he governed Arkansas.

“If Bush and Huckabee run their campaigns as if they are just picking up from when they left office at the end of 2006, they won’t succeed,” said William Kristol, editor of The Weekly Standard. “But they are both smart enough to probably understand that.”

Each has taken steps to accommodate today’s Republican Party. Mr. Bush has not retreated from his support for the Common Core, but after mocking those in his party who reversed their position on the standards in April he recalibrated his view in a November speech, saying, “Nobody in this debate has a bad motive.”

And in unveiling his political action committee this week — promoted via “Smartphone Video,” as his website noted — Mr. Bush posted a message that mixed his commitment to an immigration overhaul and education standards with pledges to “protect liberty” and “re-limit government.”

“We believe the income gap is real, but that only conservative principles can solve it by removing the barriers to upward mobility,” he wrote.

Mr. Huckabee has been even more aggressive in shifting from some of his pre-Obama positions that are now seen as heresies. He calls Common Core “toxic” and says he supports only voluntary cap-and-trade compliance.

He has taken a tougher tone on immigration, too. He was unapologetic in 2008 when Mitt Romney attacked him for allowing children of illegal immigrants to earn in-state college tuition and scholarships in Arkansas, but he has moved to harness conservative anger over the issue. He said in Iowa last year that Mr. Obama “doesn’t believe there should be borders” and alluded to a criminal element coming into the country illegally.

“It’s insanity to believe that the only people crossing our borders are coming to pick tomatoes or lay brick,” Mr. Huckabee told The Daily Beast.

Greg Mueller, a longtime conservative communications strategist and veteran of Pat Buchanan’s presidential campaigns, said each candidate would have to respond to party activists who have been deeply angered by Mr. Obama’s presidency.

“The reaction to Obama is a more energized and passionate call for limited government and freedom and returning power from Washington bureaucrats,” Mr. Mueller said. “That’s going to be the echo you’ll hear from all these guys.”

While Mr. Obama has been the galvanizing force for the party’s shift, its roots can be found in George W. Bush’s record of enlarging the federal role in education, expanding Medicare and generally increasing spending along with a Republican-dominated Congress.

“The Bush years caused a lot of conservatives to be reminded that there’s a difference between conservatives and the Republican Party,” said Michael A. Needham, chief executive of Heritage Action, a conservative advocacy group.

Mr. Bush’s professed compassionate conservatism was itself partly a reaction to Bill Clinton’s presidency, which operated under the premise that, as Mr. Clinton once said, “the era of big government is over,” but which nonetheless portrayed Republicans as harsh and uncaring.

“The tug of war in the party now is between people who think individual liberty and limited government are central and those still fighting the last war and how to win the ‘who cares about you’ argument,” Mr. Domenech said.