President Donald Trump went on the offense against Rep. Adam Schiff on Twitter Monday, calling the top Democrat on the House Intelligence Committee “sleazy” amid the committee’s high-profile probe of Russian interference in November’s presidential election.

“Sleazy Adam Schiff, the totally biased Congressman looking into “Russia,” spends all of his time on television pushing the Dem loss excuse!” Trump tweeted out Monday morning.

Schiff, a lead investigator in the Russia probe, fired back with a strong critique of his own.

“With respect Mr. President, the problem is how often you watch TV, and that your comments and actions are beneath the dignity of the office,” Schiff responded on Twitter.

Monday was the first time that Trump had criticized the nationally known Democratic congressman from Burbank in a tweet, though Schiff has previously been called out by then-White House Press Secretary Sean Spicer during a daily press briefing. The congressman, a former prosecutor, was also criticized by Kellyanne Conway, the counselor to the president, during a television interview last week.

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The House Intelligence Committee, which is investigating Russian meddling in the U.S. election as well as potential collusion with Russia by Trump’s campaign, is scheduled to interview Trump’s son-in-law and senior White House adviser, Jared Kushner, on Tuesday.