Rasmussen’s daily tracking poll has good news for Republicans, and two of the Republican candidates.  The ongoing daily survey of 500 likely voters shows Barack Obama’s job approval at 44/54, the lowest since the end of December in this series, and both Mitt Romney and Rick Santorum have leads in head-to-head matchups:

Looking at Tuesday’s upcoming primaries, the GOP race in Alabama is essentially a three-way tie, while Mitt Romney leads by eight in Mississippi.   Nationally, Romney now leads Rick Santorum by 12 points.  Regardless of who they want to win, 80% of Republican Primary Voters nationwide believe Romney will be the party’s nominee.

With the perception growing that he will be the GOP nominee, Romney leads President Obama by five points in a hypothetical 2012 matchup. Today’s numbers show Romney at 48%, Obama at 43%. That’s Romney’s largest lead since December. Matchup results are updated daily at 9:30 a.m. Eastern (sign up for free daily e-mail update).

If Santorum is the Republican nominee, he is up by one point over the president, 46% to 45%. This is the second time since polling began in 2011 that Santorum has had a slight lead over Obama. Romney is the only other candidate to lead the president more than one time in the polls. See tracking history   for Obama vs. all four Republican candidates.

Obama still beats Newt Gingrich by eight points (48/40) and Ron Paul by two (43/41), but Obama’s position has eroded against three of the four Republicans over the last few weeks.  A month ago, Obama led Romney by 10, 50/40, and Romney’s 48% today is his strongest in the series.  Against Santorum, Obama led by eight at the same time (49/41), and Santorum’s 46% is also his best in the series.  Three weeks ago against Gingrich, Obama led 51/37, but Gingrich hasn’t come close to his peak in the series of 48% at the beginning of January.  Two weeks ago Paul hit 43% for his best showing and eclipsed Obama by two, but that has been the only lead he has had in head-to-head matchups.

As I’ve noted on several occasions, these kind of matchups are apples-to-oranges comparisons, as Democrats are already united behind Obama as a nominee.  The internal divisions of a primary will handicap each Republican in the matchup, and yet Obama can’t stay above either Romney or Santorum, and now has dropped behind Romney farther than the MOE.  When Republicans finally unite behind a candidate, this suggests that Obama will find himself even more at a disadvantage, and that the election still continues to be a referendum on his performance.