An informal adviser to Mitt Romney told MSNBC on Tuesday that the campaign was being extra careful about selecting a female vice presidential candidate because of former Alaska Gov. Sarah Palin.

"I think, unfortunately, Palin poisoned the well on that," the unnamed informal Romney adviser said. "I would guess if I were inside the Romney mind that they're worried that any woman chosen will be subjected to a higher level of scrutiny."

The Romney campaign is concerned picking a female vice presidential candidate would draw comparisons with the failed McCain/Palin campaign in 2008, according to the informal adviser. Palin's critics have accused her of sinking the chances of McCain's presidency by alienating independent voters.

At least one woman, New Hampshire Sen. Kelly Ayotte (R), is being considered to run alongside Romney.

Former Minnesota Gov. Tim Pawlenty, Florida Sen. Marco Rubio, Ohio Sen. Rob Portman, Wisconsin Rep. Paul Ryan, and New Jersey Gov. Chris Christie have also been floated as possible vice presidential candidates.