Rove, who was President George W. Bush's top political adviser, said the Illinois senator's standing in the polls -- in which he generally leads likely Republican nominee John McCain by a few points -- shows voters have "grave doubts" about Obama.

"With a restive electorate, with an economy that's sort of chugging around, with a war in the background, at the end of eight years of Republican rule in the White House, Obama should be way ahead," Rove said in an appearance on CBS' "Face the Nation."

Rove said he thinks Obama is likely to pick a vice-presidential running mate who will help him politically, but who might not be ready to step into the presidency if necessary.

"I think he's going to make an intensely political choice, not a governing choice," Rove said. "He's going to view this through the prism of a candidate, not through the prism of president; that is to say, he's going to pick somebody that he thinks will on the margin help him in a state like Indiana or Missouri or Virginia. He's not going to be thinking big and broad about the responsibilities of president."