Des Moines, Iowa (CNN) Former Vice President Joe Biden expressed deep skepticism of the leftward tilt of the Democratic Party in an exclusive interview with CNN airing Friday.

Biden, speaking with CNN's Chris Cuomo in Des Moines, Iowa, suggested that " Medicare for All " is irrational, argued that the majority of Democrats are "center left" not "way left," and said Rep. Alexandria Ocasio-Cortez , while "brilliant" and "bright," did not represent Democrats who can win a general election in a competitive district or state.

The interview made clear that Biden, who is facing criticism from the left of the party amid an increasingly contentious Democratic primary , does not feel the need to sway to the left to capture the party's base and, instead, hopes to set himself apart by embracing his moderation.

Biden backed up that confidence by pointing to the 2018 midterm elections , where a host of swing districts were won by more moderate Democrats.

"That's what this election is about. I'm happy to debate that issue and all those issues with my friends because guess what, look who won the races. Look who won last time out," Biden said. "By the way, I think Ocasio-Cortez is a brilliant, bright woman, but she won a primary. In the general election fights, who won? Mainstream Democrats who are very progressive on social issues and very strong on education and healthcare."

Later on Friday, fellow 2020 candidate Sen. Bernie Sanders came to the congresswoman's defense, with Ocasio-Cortez thanking him for his support.

"I'm proud to be working with @AOC and so many other Democrats to pass Medicare for All, debt free college and a Green New Deal," Sanders tweeted Friday in response to news of Biden's comments. "This is the agenda America needs — and that will energize voters to defeat Donald Trump."

Ocasio-Cortez replied on Twitter , "Thank you, @SenSanders. It's an honor to work alongside you and the millions of other people fighting for education, healthcare, and a living wage as rights."

Ocasio-Cortez has risen to liberal stardom after she unseated Democratic Rep. Joe Crowley in New York's 14th Congressional District primary in 2018. After winning the general election easily in a reliably Democratic district, Ocasio-Cortez has swept into Congress and pushed a litany of progressive policies, all while garnering considerable media attention.

Biden's comments on Ocasio-Cortez get at the heart of a debate inside the Democratic Party: While liberal icons, including a number of newly elected members, grab headlines, the party swept into the majority in the House on the backs of more moderate members who won in swing districts.

"I wish I'd been labeled as moderate when I was running in Delaware back in the day," Biden joked.

Describing the party, the former vice president said, "Look, it's center left, that's where I am. Where it's not is way left."

Biden's clearest policy difference with the left -- health care -- was evident during the interview, too.

"I have a plan how to do that that's rational, that will cost a hell of a lot less and that will work," Biden said about health care, slamming Medicare for All, the liberal-backed proposal that would mandate Medicare as the single-payer system for all Americans. Biden, despite talking about health care on the trail, has yet to roll out a formal plan, but a number of his Democratic opponents in 2020, like Vermont Sen. Bernie Sanders and Massachusetts Sen. Elizabeth Warren, have fully embraced Medicare for All.

Biden said he would not abolish private insurance but would offer Medicare as "an option for anybody who in fact wants to buy into Medicare for All."

"But if they like their employer-based insurance, which a lot of unions broke their neck to get, a lot of people like theirs, they shouldn't have to give it up," Biden said.

The former vice president added that if Medicare for All were to pass, the country would "have 300 million people landing on a health care plan. How long is that going to take? What's it going to do?"

But that was not the extent of Biden's disagreements on policy with the left of the party.

The former vice president also said he doesn't believe "in the way" that other Democratic presidential hopefuls are proposing most liberal policies, including tuition-free college with the cancellation of all student loan debt.

He also took issue with decriminalizing crossing the border without documentation, an idea first floated by former Housing and Urban Development Secretary Julian Castro as a way to stop separating families at the US-Mexico border.

"No, I don't. No, I don't," Biden said when asked if he agreed with the plan. "I think people should have to get in line, but if people are coming because they're actually seeking asylum, they should have a chance to make their case."

Biden's task is now to convince Americans that his brand of politics has a better chance of defeating President Donald Trump in 2020.

One way that many Democrats believe he could better his chances is by picking a woman as his possible vice president, should he win the nomination.

Biden said he didn't want to be presumptive by saying he will or won't pick a certain person as vice president, but added, "I think it'd be great to have a female vice president and if I don't win, it'd be great to have a female president."