WASHINGTON (AP) — The GOP presidential field apparently set, Republican primary voters are likely facing a choice between an experienced, establishment candidate in Mitt Romney and an insurgent presidential campaign novice in Rick Perry.

With three months until voting begins, that's the dynamic that's starting to emerge now that former Alaska Gov. Sarah Palin and New Jersey Gov. Chris Christie have said they won't run for president in 2012.

Their decisions — announced over the past two days — mean it's all but certain that the Republican nominee will come from the current crop of candidates despite earlier hunger within the party for more options.

For now at least, the race is focused on Romney, the former Massachusetts governor who lost the Republican nomination in 2008 and in recent days has started to shore up support among long-time party leaders, and Perry, the Texas governor who has emerged as the top challenger despite a rocky few weeks that have stoked concerns among GOP elders about whether he's ready to take on President Barack Obama.

The dynamic is familiar.

In 2000, Arizona Sen. John McCain mounted an unexpectedly fierce challenge to George W. Bush, who had the backing of much of the Republican establishment. McCain won the New Hampshire primary but lost the nomination to Bush.

Eight years later, McCain ran for the party nomination a second time and, early on, struck a tone of inevitability and got many party leaders to support his bid. He flamed out for a while and former Arkansas Gov. Mike Huckabee, who hadn't run for president before, came out of nowhere to win the Iowa caucuses. Huckabee briefly emerged as the alternative to McCain, but the Arizona senator eventually won the nomination.

This year, a segment of the party's conservative base has been eagerly rallying around candidate after candidate without finding a favorite. They flirted with real estate mogul Donald Trump; they backed Minnesota Rep. Michele Bachmann in a key test vote in Iowa; now they're driving a surge in polling for businessman Herman Cain.

Christie's backers, who include many party elders and long-time donors, and Palin's ardent fans had been waiting to see whether either of them would run.

Now that neither of them are, those supporters are free to choose sides. It's unclear where they will turn.

In bowing out of a bid, Palin, whose unconventional style and sheer celebrity would have been an unpredictable but unquestionable force in the primary season, made clear she still would try to have a voice in the 2012 race.

"You don't need a title to make a difference in this country," Palin said Wednesday. She declined to endorse anyone but indicated she would back the eventual nominee.

It's unclear whether her backers will heed her advice. Many turned to social networking sites to assail her decision.

Romney, meanwhile, is pursuing Christie's supporters, with some success. Several high-profile figures backed him after Christie's announcement Tuesday, including New York financier John Catsimatidis and Home Depot co-founder Ken Langone.

Romney has a strong case to make. He has national name recognition and a top-notch national campaign staff. He has a national fundraising network. His weaknesses already have been vetted and he has been able to dispatch questions about them. He's built a strong campaign in New Hampshire and is quietly organizing in Iowa, where he learned from the mistakes he made last time and is working to keep expectations low. He's racking up endorsements in key states like Florida. And while he's had trouble winning over the restless conservative base, he can argue that his even-keeled campaign can take its well-honed economic message and use it to beat Obama.

But what Romney hasn't shown is that he can gain from Perry's stumbles. The latest Washington Post-ABC news poll of Republicans found Romney's popularity unchanged at 25 percent. Perry dropped to 16 percent from a previous survey, tied with Cain, the former pizza executive who has surged in recent weeks.

"Nobody wants to put a candidate forward just because they happen to be the most electable," veteran campaign consultant Terry Nelson said.

Perry announced Tuesday that he had raised more than $17 million in the first six weeks of his presidential bid. He has a third-party SuperPAC to raise outside funds, so he potentially could match a similar effort by Romney's team. On Tuesday, he earned the support of a prominent Christie backer in Iowa. And much of his support comes from the tea party Republicans — a group in part defined by their opposition to establishment politics — who are driving Republican enthusiasm in 2012. An August AP-GfK poll showed 74 percent of tea party backers viewed Perry positively.

But because he's the new guy, most voters are still learning who Perry is. His inexperience has shone through, and it's already driving doubts about his candidacy and left him to prove to both voters and to party insiders that he's ready to be president.

Perry stumbled in recent debates. On the campaign trail, he's been pushed off his core message about jobs in Texas by voter questions about immigration, Social Security and other issues that are of less concern to voters.

And he's behind Romney in setting up campaign organizations in Iowa, New Hampshire and other early voting states. That's a weakness made even worse by an accelerating primary election calendar. Nevada Republicans announced Wednesday they will hold their caucuses Jan. 14. That's likely to push the New Hampshire primary up to early January and could mean Iowa caucus-goers meet in December.