Attorney General William Barr revealed Tuesday that he is reviewing the “conduct” of the FBI’s original Russia investigation during the summer of 2016, following calls from Republicans to investigate the origins of the probe.

Barr testified before a congressional panel in what was his first Capitol Hill appearance since revealing the central findings of Special Counsel Robert Mueller’s investigation. Barr was grilled by Democrats on the handling of that summary, which stated the special counsel found no evidence of collusion between members of the Trump campaign and Russia during the 2016 election — but he was also questioned about the initial Foreign Intelligence Surveillance Act (FISA) warrants approved to surveil members of the Trump campaign.