President Barack Obama's approval rating has enjoyed a modest bump since the Democratic National Convention, while Mitt Romney is already behind in the presidential debate game, according to a national polls conducted by CNN/ORC International released Monday.

Obama's approval rating increased to 51 percent from 48 percent since the convention began last week, according to the poll. The increase falls within the expected range of "post-convention bumps," when the featured candidate enjoys a boost from several days of verbal pats on the back.

The approval rating jump explains a CNN poll released Monday which showed Obama pulling away slightly from Romney, leading 52 to 46 percent. Several polls, including Gallup, ABC/Washington Post and Rasmussen all showed Obama at varying degrees of improved strength against Romney, averaging a three-point gain since he formally accepted his party's nomination Thursday.

"The Democratic Convention was fairly well received, particularly in comparison to the GOP meeting the previous week in Tampa," CNN Polling Director Keating Holland said.

Likely voters give the incumbent a 25-point lead, 59 to 34 percent, over the former Massachusetts governor when asked who will do a better job in the three debates slated for October, according to the poll.

Romney is not known for pyrotechnic stints before the podium, and suffers from the juxtaposition of his commendable but staid convention speech with Obama's trademark staggered, preacher-like delivery.

The GOP standardbearer's flaws are conceded by some in his own party. Eighteen percent of Republican voters expected Obama to "win" the debates, while only 5 percent of Democrats thought the GOP nominee would win.

The presidential debates will be held on Oct. 3, Oct. 16 and Oct. 22.