The rise of the "tea party" movement, with its contempt for convention, has undermined the tradition of bestowing the nomination on the candidate presumed next in line, who usually paid their dues through long service or a previous White House try.
The rise of so-called super PACs, independent political financing organizations unfettered by spending limits, also means that a candidate can stay competitive long after their campaign's donor base taps out, potentially extending the race beyond the first few contests.
The upshot is a GOP nominating race that is at least as unsettled as the competition four years ago, when Sen. John McCain of Arizona rose from the political graveyard and rallied to claim the nomination.
"We knew from the beginning this was going to be one of the most competitive nominating fights we've had," said Dick Wadhams, a Republican strategist who is neutral in the race. "We thought we had one back in 2008, but this one has already taken on more twists and turns than anything that happened in '08."
After six debates and a succession of candidates atop the polls — including, at various times, Donald Trump, Mitt Romney and Rick Perry — the contest has essentially settled into a two-man contest between former Massachusetts Gov. Romney, who ran in 2008 and never stopped, and Texas Gov. Perry, who jumped into the race less than two months ago.
Neither, however, is anything close to a prohibitive front-runner.
Although he maintains a following in Iowa, the state voting first, and in New Hampshire, where he owns a home, Romney consistently polls in the middling 25% to 30% range nationally. More significantly, he has yet to win over many in the GOP establishment, which continues to clamor for new alternatives, most recently New Jersey Gov. Chris Christie.
Part of the reason is Romney's shift from the moderate he was in Massachusetts to the much more conservative candidate he became in 2008, a move that put him more in line with GOP orthodoxy but raised doubts about his core beliefs. Part of it is also what many consider a distinctly lackluster candidacy.
"He's running a perfectly safe, bland, me-too campaign," said Jan van Lohuizen, who conducted polling for Romney in his last presidential race but is unaffiliated this year. "I haven't heard him say anything interesting in the five years he's been running."
Perry surged to the top of national polls after entering the race in August. But he's stumbled since, after a beating stemming in part from his description of Social Security as a failure and his suggestion that those who criticized Texas' taxpayer-supported college tuition for illegal immigrants were heartless. He retracted the latter statement after days of outrage from conservative activists.
"What he has to show is that he has the skills to operate at a national level — and he may well," said Rep. Peter T. King (R-N.Y.), reflecting widespread nervousness among Republican lawmakers who would have to run with Perry atop the GOP ticket in 2012.
Some things remain unchanged. Iowa and New Hampshire remain the two most critical early-voting contests, given their one-two place on the calendar and the powerful momentum they can generate for the winners.
Rep. Michele Bachmann of Minnesota, who briefly climbed in polls after topping a summer straw poll of Iowa activists, almost certainly has to win the state's caucuses to remain viable. Former Utah Gov. Jon Huntsman Jr., who has fallen well short of the hype that preceded his June entry in the race, is staking everything on the New Hampshire primary.
A candidate winning both Iowa and New Hampshire could go a long way toward wrapping up the contest by mid- to late January, depending on when the voting begins. But no Republican, other than a sitting president, has ever done that.
Moreover, the party's new nominating rules mean a losing candidate can still walk away with a generous share of delegates, keeping their chances alive. Adopting a system used by Democrats, GOP leaders changed the rules last year, hoping to prevent a rush to judgment and give the eventual nominee more time to campaign nationwide.
Today, however, some party strategists curse the rules, noting that President Obama is already raising money and organizing for the general election. Others believe a lengthy competition won't necessarily hurt the GOP nominee.
"It will force the candidates to rise to the occasion of this competition," said Wadhams, a former Colorado Republican Party chairman.
One thing that won't be lacking in the primary fight is money, thanks to the 2010 Supreme Court decision that removed restrictions on union and corporate spending and allowed individuals to make unlimited super-PAC contributions, in contrast to the $2,500 ceiling on giving to candidates.
Both Perry and Romney have super-PACs supporting their campaigns; Romney's has already reported $20 million in contributions.
The combination of new campaign finance rules and a more generous apportionment of delegates leads many to suspect the GOP race will last much longer than the relatively brief contests of the past 30-plus years.
"Both Romney and Perry appear that they will have well-run, well-funded campaigns that could be splitting delegates in March and April," said Scott Reed, an unaffiliated Republican strategist. "This nominating fight has the potential to go into May."
The last big day of the primary season is June 5, when California and Christie's New Jersey vote.
Barabak reported from San Francisco and West from Washington.