"I think this GOP primary ... has been a race to the bottom. We have seen nastiness, divisiveness, ugliness, distortions of opponents' records, of the president's records," President Obama's campaign adviser Robert Gibbs said in an interview on ABC's "This Week."
"You just heard John McCain say it. It's affecting their standing, their own candidates' standing with the American people. We see it in their turnout numbers. Fewer and fewer Republicans are coming out to even participate in the process of nominating somebody to run against President Obama."
Gibbs said he doesn't think differing opinions on the issues should be met with personal and character attacks, pointing to GOP nomination hopeful Rick Santorum's questioning of Obama's faith Saturday.
Sen. McCain, R-Ariz., said on "This Week" he's concerned the GOP race has gotten so nasty Obama will have an easier time being re-elected.
"And I think there's reason to be concerned about it. I've been in very tough campaigns. I don't think I've seen one that was as personal and as characterized by so many attacks as these are. And, frankly, one of the reasons is the super PACs," he said.
McCain said the super PACs' access to unlimited money is a major reason attack ads have flourished during the campaign.