Former Sen. Claire McCaskill, D-Mo., called Sen. Rand Paul, R-Ky., "kind of an idiot" over his comments about the whistleblower who reported on President Trump's July call with the president of Ukraine.

"Who cares about the whistleblower?" McCaskill asked during an appearance on "Morning Joe" Tuesday. "I mean seriously, it is so irrelevant at this point."

When MSNBC host Mika Brzezinski claimed Paul said it "really matters," McCaskill dismissed his concerns: "Well, Rand Paul's just kind of an idiot about stuff. I mean, this is like so silly ... we all know that the whistleblower's account has been corroborated by information directly from the White House."

GRAHAM: WE NEED THE WHISTLEBLOWER'S NAME, WE NEED TO CROSS-EXAMINE

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Paul's office did not respond to Fox News' request for comment. During a rally in Lexington on Monday, Paul called on media outlets to publish the whistleblower's identity.

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Paul alleged on Twitter that the whistleblower was former Vice President Joe Biden's "point man" on Ukraine.

"It is being reported that the whistleblower was Joe Biden’s point man on Ukraine," he tweeted, linking to an article on the whistleblower. "It is imperative the whistleblower is subpoenaed and asked under oath about Hunter Biden and corruption."

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But for McCaskill, there was "just one question left: Is this okay?" She seemed to refer to Trump requesting that Ukraine investigate Biden.

Democrats have opened an impeachment inquiry, alleging the president pressured Ukraine to interfere with the 2020 presidential election. President Trump has denied any wrongdoing and claimed that the call was a legitimate exercise of his authority.