Omar claimed McCain and other conservatives regularly use anti-Muslim smears against her online.
“The same people who chastise the progressive movement regularly traffic in anti-Muslim smears and hate speech against me and those I represent,” Omar, who has endorsed Sanders, tweeted. “It’s almost as if they don't genuinely care about online harassment."
After Sanders was criticized at Wednesday’s Democratic debate of not effectively curbing social media harassment by some of his most aggressive supporters, McCain weighed in on Twitter.
“Bernie - your army of Bernie bro’s are the worst in all of the internet and every woman on both sides knows it," McCain wrote. "Mysoginistic, abusive and inspired by you. There’s no army of Pete bots or Biden bots abusing women!”
Omar then tweeted a screenshot of McCain’s tweet plus another in which the TV host retweeted an unsubstantiated claim that Omar had married her own brother.
"How is this not a bigger deal?" McCain wrote.
The congresswoman has strenuously denied the claim, which she calls “disgusting lies.”
This isn't the first time the two have clashed.
Last year, McCain said Omar’s rhetoric -- that some have called anti-Semitic -- needed to be addressed following a deadly shooting at a synagogue in Southern California.
“I do think when we are having conversations about anti-Semitism we should be looking at the most extreme on both sides, and I would bring up Congresswoman Ilhan Omar and some of her comments that got so much attention,” McCain told ABC News' George Stephanopoulos.
Omar, who has apologized for some tweets perceived as anti-Semitic, simply responded, “Oh, bless her heart!”