Republican South Carolina Sen. Lindsey Graham promised that he will launch his own “deep dive” inquiry into the origins of the Trump-Russia investigation after the conclusion of Justice Department Inspector General Michael Horowitz’s investigation into alleged abuse of the Foreign Intelligence Surveillance Act.

“I promise your listeners, after Horowitz issues his report about the flawed FISA warrant, I’m going to deep-dive into how this stuff started,” the Senate Judiciary Committee chairman said while appearing on Sunday Morning Futures on Fox News this morning. “How could it go so far if there was no collusion?”

Special counsel Robert Mueller concluded that although the Russians did interfere in the 2016 presidential election, he could not establish any criminal collusion between the Russian government and the Trump campaign. He will be testifying in front of Congress on July 24.

Graham, speaking with Maria Bartiromo, said that the probe by the Justice Department and FBI into possible ties between the Trump campaign and Russia that began under President Obama was a “politicized investigation.” Citing what he said is a clear double standard, Graham contrasted the Justice Department’s “kid-gloves” investigation of Hillary Clinton’s use of an illicit private server with their all-out investigation of Trump-Russia collusion.