At least so far, Gallup keeps giving Rick Santorum good news on the electability issue.  In their latest poll, both Santorum and Mitt Romney fall within the margin of error against Barack Obama, and Romney actually bests Obama slightly [see update]:

U.S. registered voters are closely divided in their 2012 presidential election preferences between Barack Obama and Mitt Romney, and between Obama and Rick Santorum. Romney is slightly ahead of Obama, 50% to 46%, while Obama edges Santorum, 49% to 48%, but neither of these differences is statistically significant.

Santorum and Romney are the current leaders in the volatile Republican primary race. In Gallup Daily tracking conducted Feb. 17-21, 35% of Republican voters nationwide support Santorum, compared with 27% for Romney, 15% for Newt Gingrich, and 10% for Ron Paul.

Santorum’s competitive position against Obama in the Feb. 16-19 data represents an improvement compared with interviewing conducted Jan. 27-28, when Obama led Santorum by eight percentage points, 51% to 43%. At that time, Santorum was still trailing both Romney and Gingrich in Gallup’s tracking of Republican preferences for their party’s nomination. After his Feb. 7 wins in Minnesota, Colorado, and Missouri, Santorum surged to a 10-point lead over Romney. He continues to lead the race among Republicans nationally, and may now be more competitive with Obama among all U.S. voters as a result.

Santorum’s numbers are moving up, while Romney’s remain relatively stable.  That is good news for both Republicans, but bad news for Obama.  While Republicans fight each other, Obama’s stature should give him more of a lead over the GOP pack.  Instead, Obama can’t get to 50% against a split field, which portends a very tough re-election campaign once Republicans settle on the nominee.

Santorum got more good news out of Michigan today, albeit qualified.  The new Detroit Free Press-WXYZ poll in the state shows Santorum with a narrow three-point lead over Romney, but that’s a decline from earlier polls in Michigan:

A week of personal appearances, newspaper op-eds, robocalls and television ads has brought Mitt Romney back within striking distance of national frontrunner Rick Santorum in Michigan’s Republican presidential primary, but with six days to go Santorum’s upstart campaign remains on the verge of what could be a defining victory in Romney’s birth state, a Detroit Free Press-WXYZ-TV poll shows. …

Santorum continues to show strength, as the conservative base rallies around him: Among self-described conservatives, he leads Romney 46% to 27% (Romney leads among the much-smaller bloc of moderate voters 51% to 17%.) Men favor Santorum 41% to 29% for Romney, and Santorum has built up double-digit leads over Romney in the western and central parts of the state.

Romney has a double-digit lead in Detroit, which is something to watch on Tuesday night when returns start to come in.  If the race remains this close, though, it may not matter as much as one would think.  Michigan allocates its 30 delegates on a proportional basis, 28 on how their Congressional districts vote.  It may be possible for one of the candidates to win more delegates even if they narrowly lose the overall popular vote, or to break even on delegates.  The psychological impact of the win on the following Super Tuesday races is what will be most important, but Santorum might end up benefiting from a split decision.

Arizona, however, is winner-take-all.  So far, Romney seems in control of the Arizona primary, and it may be that a split decision in Michigan will make the Arizona contest that much more meaningful on Super Tuesday.

Update: I misread the Gallup results of the head-to-head between Romney and Obama.  Romney’s ahead by 4 (still within the MOE).  I’ve corrected the opening paragraph and apologize for the error.  Thanks to Jon A for pointing it out to me.