Mitt Romney has a sizeable lead in 15 battleground states, according to a CNN/ORC poll released late Monday.

The Republican candidate leads President Obama 51 percent to 43 in 15 states that will be critical in determining the outcome of the 2012 election.

Obama won 12 of these battleground states in 2008 — Colorado, Florida, Iowa, Michigan, Nevada, New Hampshire, New Mexico, North Carolina, Ohio, Pennsylvania, Virginia and Wisconsin — and will need to keep about half of those in 2012 if he’s to secure reelection. The poll also included Missouri, Indiana and Arizona as battleground states.

That’s good news for Romney, showing he has a base of support in those states, though the blanket poll of 534 registered voters doesn’t give an indication of which candidate leads in an individual state, or by how much.

Two polls released last week showed Obama with an edge in several swing states. An NBC News/Wall Street Journal survey found Obama leading Romney 50 percent to 42 among likely voters in 12 battlegrounds, and a Quinnipiac University poll found Obama leading Romney by 9 points in Ohio, 6 in Pennsylvania and 4 in Florida. 

Obama holds a slim lead over Romney nationally in the CNN/ORC poll, 49 percent to 46, which is within the poll’s margin of error and unchanged from the same poll in May.

Democrats, however, have seen a spike in enthusiasm since the Supreme Court’s decision to uphold the bulk of Obama’s healthcare law. Fifty-nine percent of those polled they were very enthusiastic about voting, up from only 46 percent in March, while Republican enthusiasm has remained steady at 51.

And despite most polls showing Obama’s healthcare law to be unpopular, voters say Obama would do a better job on healthcare than Romney, 51 percent to 44.

CNN polled 1,390 registered voters across the country and 534 registered voters in 15 battleground states. It was conducted between June 28 and July 1 and has a 2.5-point margin of error.