President Barack Obama's reelection team twisted the knife in Mitt Romney Monday, seeking to deepen the misery for the wounded Republican White House front-runner as crucial new tests loomed.

Obama campaign manager Jim Messina launched an assault on Romney, and gave his insurgent challenger Newt Gingrich a pass, in a clear sign the president's brain trust would rather face the volatile former House speaker in November.

"The bottom line is this: the more voters learn about Romney, the more unfavorably they view him," Messina said in a memo issued two days after Gingrich won the latest Republican nominating contest, in South Carolina.

Romney, the establishment Republican pick, awoke Monday with just over a week to slow Gingrich's momentum ahead of the Florida primary on January 31, and Messina's shot appeared to be an attempt to complicate his efforts.

"This week Florida's voters will meet a candidate with no core values who believes he's entitled to play by a different set of rules," he said, pressing a campaign narrative that Romney is a mere cipher for the wealthy.

"Like their predecessors in the other early states, they will see a career politician willing to say and stand for anything to get elected and (who) is out of touch with working and middle-class Americans.

"Mitt Romney prides himself on being a great businessman. But the American people aren't buying what he's selling," Messina said hours before the Republican candidates clash in their latest debate in Tampa, Florida.

Recent opinion polls suggest that Obama would face a tough fight against Romney in a general election, with the result of the race locked within a few points.

The former Massachusetts governor has long been seen as the most effective messenger for a critique of Obama on the key issue : jobs -- at least he was until a furor erupted last week over his record as a venture capitalist.

Obama handily leads in national polls over Gingrich, who is considered less likely to attract key independent voters and has a controversial past which could cloud Republican efforts to make the election a referendum on the president's economic record.

Messina's broadside also represented an opening shot in the fight for the crucial state of Florida in November.

If Obama wins the Sunshine State, which has 29 of the 270 electoral votes needed to claim the White House, his path to reelection could be all but assured.

Mochila insert follows ...