PRINCETON, NJ -- The topsy-turvy Republican presidential race has taken another turn, this time in Mitt Romney's favor. Romney now holds a 32% to 28% advantage over Rick Santorum after Santorum led for most of the last 10 days, including a 10-percentage-point advantage a week ago. Newt Gingrich and Ron Paul remain well behind Romney and Santorum.

The latest results are based on Feb. 22-26 Gallup Daily tracking interviews with 1,160 Republicans and Republican-leaning independents nationwide who are registered to vote. They show Romney gaining momentum nationally heading into Tuesday's important Michigan and Arizona primaries, the first contests in nearly three weeks. Santorum surged to his first lead in Gallup's tracking after he swept the Feb. 7 contests in Missouri, Minnesota, and Colorado. Santorum's decline in recent days has come as Romney and Paul, in particular, have stepped up their criticism of his voting record in Congress and his positions on issues.

Santorum, along with Romney, Gingrich, Rick Perry, and Herman Cain, have all held or shared the lead at some point in Republican nomination preference polling since the field began to take shape last spring. The list of five leaders does not include three potential candidates who were among the leaders in a Gallup poll at some point in late 2010 or early 2011 but ultimately decided not to run -- Mike Huckabee, Donald Trump, and Sarah Palin.

Prior GOP nomination campaigns were much more orderly, typically having one dominant front-runner for much if not all of the campaign. Since the nominating power was moved from convention delegates to voters in state primaries and caucuses in 1972, the 2008 nominating contest had been the most volatile prior to this year's, with three different national leaders during the campaign -- Rudy Giuliani, Huckabee, and eventual winner John McCain.

Romney Gains Among Conservatives

In general, Romney's support has increased among nearly all subgroups of Republicans in recent days. But his gain and Santorum's decline have been especially evident among self-identified conservative Republicans.

Whereas Santorum led by 22 points (44% to 22%) among this group on Feb. 20, the two are now essentially even, with Santorum at 33% and Romney at 29%. Meanwhile, Romney continues to be the strong favorite of moderate or liberal Republicans, whose preferences have been more stable over the past 10 days.

Santorum's support has also taken a hit among regular churchgoers, a group crucial to his coalition, though he retains a numerical advantage over Romney within this group.

Implications

The Republican nomination contest is entering a crucial phase with the Michigan and Arizona primaries on Tuesday and 10 state primaries or caucuses on March 6. To the extent Romney, Santorum, or one of the other candidates wins the bulk of these contests, he will likely emerge as the strong front-runner for the GOP nomination.

Although the lead has changed hands a number of times over the course of the campaign, Romney has been consistently near the top. His standing suggests he is perhaps not embraced enough by the party to emerge as the clear and consistent front-runner, but he has been better able than his rivals to withstand the scrutiny that comes with being a leading contender for the nomination.

Sign up to get Election 2012 news stories from Gallup as soon as they are published.