(CNN) - In the final weekend before Iowa voters kick off the presidential primary season, Democrats Barack Obama and Hillary Clinton each raised questions about the other's ability to beat the Republican Party's nominee next November.
"We are less likely to win an election that starts off with half the country not wanting to vote for that candidate," Obama said Saturday at an event in Madison.
"We are less likely also to win an election with somebody who had one set of positions four years ago and has almost entirely different positions four years later. We've been through that," he also said in comments that seemed to be directed at John Edwards. At a later event he said the same thing and named Edwards.
Clinton quickly responded in a media availability in Eldredge, sounding her familiar campaign theme that she has already proven her ability to withstand the "Republican attack machine," and suggesting Obama has yet to be tested.
"I have been around a while," the New York Democrat said. "I have seen a lot of elections come and go, and who ever our Democratic nominee is will be subjected to the full force and effect of the Republican attack machine."
"Unfortunately that is the barrier that you have to overcome," she added. "What you know with me, I have already overcome it. I have withstood it, and not only survived it but thrived over the last 16 years. So there is very little guess work."
- CNN's Chris Welch and Mike Roselli contributed to this report