(CBS News) -- President Obama has overtaken Republican candidate Mitt Romney for the first time of the 2012 campaign in a dozen key states that swing back and forth between the parties in presidential elections, according to a poll released Monday by USA Today and Gallup.
Mr. Obama garnered 51 percent support, compared to 42 percent for Romney in the hypothetical match-up in battleground states, a sharp shift from just a month ago when the former Massachusetts governor was leading the president, 48 percent to 46 percent.
Among registered voters nationally, Mr. Obama's lead is smaller, 49 percent to 45 percent, but still the largest lead he has held over Romney. The two men were tied at 47 percent a month ago. Since August 2011, the two men have each bested the other, but neither has had more than a 2 percentage point advantage.
Mr. Obama's gains stemmed largely from women under 50, who back the president two to one over Romney. More than 60 percent of those voters support the president, compared to just 30 percent for Romney. That compares to fewer than 50 percent support for Mr. Obama and about 44 percent for Romney in mid-February.
The president has an even larger lead over increasingly likely Romney will win the nomination. Mr. Obama leads Santorum 51 percent to 43 percent among U.S. registered voters.even as it becomes
The poll showed support among self-described Democrats and Republicans is solid for both candidates, with independents the only ones who have not yet decided which candidate they will back in November. Mr. Obama has 87 percent support among Democrats and Romney has 84 percent support among Republicans. Just two percent of Democrats and three percent of Republicans are undecided.
Among independents, however, the race is much closer. The president took 48 percent of those voters, compared to 40 percent for Romney. About 12 percent of independents said they had not yet made up their mind.
Enthusiasm among voters is down for both candidates. About 42 percent of registered voters told the pollsters they are "extremely" or "very" enthusiastic about voting for Mr. Obama, ten points lower than in January.
About the same level said they were "extremely" or "very" enthusiastic in their support of Romney, 13 percentage points lower than January. In late 2011, Romney supporters' enthusiasm eclipsed Mr. Obama's supporters' enthusiasm.
The telephone survey of 901 registered voters living in all 50 U.S. states and the District of Columbia was conducted March 25-26 and has a margin of error of plus or minus 4 percentage points.
The telephone survey of 933 registered voters living in the battleground states of Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin was conducted March 20 through 26 and has a margin of error of plus or minus 4 percentage points.