“On the other side, it’s a mess,” McCaskill said on MSNBC’s “Morning Joe” when asked how Republicans in swing and red states could survive the 2014 midterms. “I mean, they are — they really have a civil war in their party right now. … You’ve got people who are willing to compromise and who understand the beauty of compromise in our democracy, and then you have people like Ted Cruz and some of the others that just think that they want to drive as hard as they can off the right edge of the world.”

McCaskill suggested the desire of conservatives to nominate conservatives like Cruz in swing states was costing the GOP chances at Senate seats.

( Also on POLITICO: Quiz: Do you know Sen. Cruz?)

“The reason I could win [was] they nominated a flawed candidate that was so extreme,” she said on MSNBC. “It wasn’t what Todd Akin said that was the problem, but what he believed. That is the base of the Republican party right now.”

Host Joe Scarborough, a former GOP congressman, said he thought extremism was on both sides of the aisle. “Oh, I agree,” McCaskill said.

A Cruz spokesman responded by suggesting McCaskill “take up Sen. Cruz’s longstanding invitation to work together — Republicans, Democrats, Libertarians and independents — on positive, pro-growth legislation to restore economic prosperity.”

Last month, McCaskill compared Cruz to the infamous red-baiting Sen. Joe McCarthy after his aggressive questioning of Defense Secretary Chuck Hagel, which drew admonishments even from other Republicans.

“He basically came out and made the accusation about money from North Korea or money from our enemies, and he just laid out there all of this accusatory verbiage without a shred of evidence,” McCaskill told The New York Times. “In this country, we had a terrible experience with innuendo and inference when Joe McCarthy hung out in the United States Senate, and I just think we have to be more careful.”