Democrats have reclaimed a big edge in enthusiasm over a Republican electorate that is dissatisfied with its presidential candidates and pessimistic about its prospects for reclaiming the White House in 2012, according to new polling from the Pew Research Center released Wednesday.

Pew President Andrew Kohut presented the findings at a Christian Science Monitor roundtable on Wednesday morning, in which he said the GOP base had become “disillusioned” and showed a “real lack of enthusiasm and commitment.”

According to Pew, Obama leads Mitt Romney 54 percent to 42 percent in a national head-to-head matchup, and he leads Rick Santorum 57 percent to 39 percent. The poll was taken March 7-11, before Santorum’s victories in the Alabama and Mississippi primaries.

The enthusiasm gap within those numbers is even greater, with 41 percent saying they support Obama strongly in a matchup against Romney, compared to only 28 percent who said the same about Romney. Against Santorum one-on-one, Obama leads the former senator 45 percent to 28 percent in enthusiasm.

“Republicans certainly don’t have the big engagement advantage they had in 2010,” Kohut said. “The mixed views Republicans have of the field has led Democrats to close the enthusiasm gap.”

There is also a seeping pessimism among Republicans about the party’s prospects for producing a candidate capable of defeating Obama in the fall, according to the Pew results.

Overall, 59 percent said Obama is likely to defeat either Romney or Santorum in November, but that sentiment is more pronounced when broken down among party lines. Eighty-three percent of Democrats believe Obama would defeat Romney, while 60 percent of Republicans believe Romney would defeat Obama.

The numbers are far worse for Santorum among Republicans; only 46 percent said they thought he would defeat Obama, while 89 percent of Democrats said they believed Obama would defeat Santorum.

In addition, the favorability ratings for Romney and Santorum are getting worse as the primary season drags on. Only 29 percent of Americans said they had a favorable view of Romney, compared to 51 percent who had an unfavorable view. Santorum is at 27 percent favorable and 44 percent unfavorable.

“No candidate has ever been elected with the kind of favorability... Romney and Santorum [have],” Kohut said. “But no president has been reelected with the unemployment rate Obama has, so one of those precedents is going to be broken.”

That should be a point of hope for Republicans, except that Obama’s favorability and job approval have steadily improved along with the economy.

Fifty-six percent now have a favorable view of Obama, compared to 41 percent unfavorable in the Pew poll.

The president’s job-approval rating has ticked up from 44 percent to 47 percent to 50 percent presently, versus 41 percent who disapprove, according to Pew.

That’s a better result than a poll released Monday by The New York Times and CBS News that found only 41 percent approve of Obama’s job performance.

Some have speculated that once that once Republicans decide on a candidate, the base will coalesce around him with the goal of defeating Obama, similar to how Democrats rallied after a bruising primary in 2008.

But the Pew numbers say that’s not necessarily the case. Support from Romney's backers doesn’t directly translate into support for Santorum, if he were to become the candidate, and vice versa.

Of the 75 percent who said they would strongly support Romney against Obama in the general election, only 55 percent of those said they would strongly support Santorum. Likewise, of the 83 percent who said they would strongly back Santorum against Obama, only 47 percent said they would do the same for Romney.

“Here we have Republicans feeling negative about their choices,” Kohut said. “In 2008, 80 percent of Democrats said they were thrilled with their choices, and they didn’t dislike the other candidates. You didn’t see this level of dissatisfaction. The fire was there to replace George W. Bush, and arguably that’s still there for Republicans (to replace Obama), but Democrats had both.”