Peter Strzok testifies before Congress

Peter Strzok, the FBI agent whose anti-Trump text messages raised concerns that the Mueller investigation was tainted by political bias, is taking questions from Congress Thursday — and things have already gotten heated.

Strzok, a veteran counterintelligence agent, oversaw the probe into Hillary Clinton’s use of a private email server in 2016, and was also involved in special counsel Robert Mueller’s investigation into whether the Trump campaign colluded with Russia to interfere with the 2016 presidential election.

Last summer, the Justice Department found that Strzok had sent text messages critical of Trump to FBI attorney Lisa Page — with whom he was having an affair — during the 2016 presidential election. Trump and many of his conservative supporters interpreted this as evidence that Strzok was plotting to interfere with the election. Mueller removed Strzok from the Russia investigation, but that hasn’t stopped lawmakers from grilling Strzok about the texts at his hearing.