A prosecutor for special counsel Robert Mueller on Monday showed his frustration with the Virginia federal judge overseeing the trial of Paul Manafort, President Donald Trump’s former campaign chairman.

Politico describes “a series of prickly clashes” between the prosecutor, Greg Andres, and U.S. District Judge T.S. Ellis III during testimony by Manafort’s former deputy, Rick Gates. According to Politico, Andres “sometimes lashed back” at the judge.

In one exchange, Ellis interrupted Andres during Gates’ testimony about his travels, according to Politico. “Let’s go to the heart of the matter,” Ellis said.

“Judge, we’ve been at the heart,” Andres began to reply before Ellis cut him off and scolded Andres for interrupting him.

Manafort prosecutor lashes back when judge tries to speed up Gates’ testimony