Clinton told ABC's "Good Morning America" he doubts Romney could rebound from a tough Republican primary and negative ratings.
"Mr. Romney has a different challenge than I did," said Clinton, a Democrat who came back to win a second term in 1996 after a difficult primary and high negative ratings. "Even though he had a bruising primary and higher negatives and I did too, mine was just one long character attack. It was a personal attack on me. You know, 'You shouldn't have this guy be president.'"
Clinton said he was able to stage a comeback because "the American people are inherently fair."
"I named Al Gore. We reintroduced our economic plan," Clinton said. "Then we reintroduced ourselves to the American people. But we never had to change what we were saying from primary to the general. The problem that Governor Romney has, is his character attack was, 'You don't really know what he believes. He did this, he says that.'"
Romney, Clinton said, has to "convince the swing voters that he'll be moderate enough and open enough and inclusive enough to be an effective president, and effective on the economy and hope that the Republican base voters say, 'Well, OK, so he maybe wasn't as right-wing as he claimed to be in the primary. Still more conservative than President Obama. I guess I'll vote for him anyway and I won't stay home.'"
Speaking of his wife, Secretary of State Hillary Clinton, he said he believes she's being "completely honest" when she says she doesn't think she'll run for president in 2016.
"I want her to do what she wants to do," he said. "I'm glad she's coming home. I miss her. We have fun together."