Two polls released Tuesday provide striking evidence of Palin's transformation over the course of two months from GOP energy boost to major drawback, as the Alaska governor's rising unfavorability ratings have become a critical vulnerability for the McCain campaign.

Palin's qualifications to be president now rank as voters' top concern about John McCain's candidacy - "ahead of continuing President Bush's policies, enacting economic policies that only benefit the rich and keeping too high of a troop presence in Iraq," according to a new NBC/Wall Street Journal poll.

Fifty-five percent of respondents now say Palin is not qualified to serve as president, a five-point jump from the previous NBC/WSJ survey.

In addition, for the first time, more voters have a negative opinion of her than a positive one. In the survey, 47 percent view her negatively, versus 38 percent who see her in a positive light.

That's a striking shift since McCain chose Palin as his running mate in early September, when she held a 47 to 27 percent positive rating.

According to another poll by Pew Research Center for the People & the Press, opinions of Palin have flipped in the last month, especially among the female voters she was expected to attract to the McCain ticket.

Nearly half -- 49% -- of voters have an unfavorable opinion of her while 44% have a favorable view. A month ago, "favorable opinions of Palin outnumbered negative ones by 54% to 32%."

Women, especially women under age 50, have become increasingly critical of Palin: 60% now express an unfavorable view of Palin, up from 36% in mid-September. Notably, opinions of Palin have a greater impact on voting intentions than do opinions of Joe Biden, Obama's running mate.