Almost three out of five Americans believe former Alaska Gov. Sarah Palin (R) would not be an effective president, a new poll found Monday.

Fifty-nine percent of U.S. adults said they don't think Palin, the 2008 Republican vice presidential candidate and potential 2012 candidate, would be an effective president of the United States.

Twenty-six percent of adults, by contrast, said they believe Palin would be effective, according to a "60 Minutes"/Vanity Fair poll conducted earlier this August.

The poll comes as a midterm election cycle nears in which Palin has made her impact, keeping her political profile high through a successful book, a commentator gig on Fox News and a series of endorsements and donations to conservative Republican candidates for office.

Palin enjoyed a particularly successful past week after Joe Miller, her endorsed Republican candidate for Senate in her native Alaska, appeared to have defeated incumbent Sen. Lisa Murkowski (R), a Palin foe, in the state's GOP primary. Palin also drew headlines this past Saturday for her speech during a rally on the National Mall organized by Fox host Glenn Beck.

But even Republicans — and conservatives within the GOP — appear split over whether Palin would be well-suited to occupy the nation's top political office.

Republicans on balance believe, 47-40 percent, that Palin would be an effective president. Forty-one percent of conservatives said they thought Palin would do well in the White House, while 40 percent said she would not — a close margin among those within the GOP who are seen as Palin's base of support.

If Palin were to run for president in 2012, she might also face difficulty in winning over independents, 63 percent of whom told the poll that Palin would not have the ability to be effective in the Oval Office. Twenty-one percent of independents said Palin would have those skills.

The poll, conducted by CBS News between Aug. 3-5, randomly surveyed 847 U.S. adults.