WARSAW, Poland (AP) — A trial opened has opened in Warsaw on claims by a conservative American political activist that he was defamed by a Polish journalist who described him as "Trump's man" and sympathetic to Russian President Vladimir Putin.

Matthew Tyrmand of the group Project Veritas brought the case against journalist Tomasz Piatek and Agora, publisher of the liberal Gazeta Wyborcza newspaper. Tyrmand is demanding an apology and 50,000 Polish zlotys ($13,000) he says he will donate to charity, if he wins.

The first person to take the witness stand Wednesday was Project Veritas founder James O'Keefe. Project Veritas carries out undercover operations in the United States which it says are aimed at uncovering wrongdoing, but the group has been criticized for its tactics.