"You are the most radical left person I've ever known. I say that with love and respect," McCain said. Behar responded by saying she took that as a "compliment."
But earlier in the program, she and co-host Whoopi Goldberg seemed perplexed as to what Republicans meant when they decried far-left or "socialist" policies emerging among Democrats.
Behar said she considers herself as a "centrist" who acts out of "common sense."
"For me, every single candidate except [former Vice President Joe] Biden is too far to the left," McCain said spit back.
Their exchange came as Democrats faced internal criticism over some politicians apparently refusing to embrace more progressive policies. Biden, in particular, received criticism on Wednesday over his support for the Hyde Amendment, a decades-old law that blocks taxpayer funding for abortion. Biden eventually reversed that position in a statement on Thursday.
When Behar pressed McCain on what policies she disagreed with, she listed several including late-term abortion -- something that Goldberg claimed didn't exist. "There is no such thing," she argued.