Senate Judiciary Chairman Lindsey Graham (R-S.C.) said at a hearing to review the findings of the Justice Department's inspector general report that it was Russia, not Ukraine, who interfered in the 2016 presidential election by hacking the Democratic National Committee.

"We know the Russians are messing in our elections. And it was the Russians, ladies and gentlemen, who stole the Democratic National Committee emails, Podesta's emails and screwed around with Hillary Clinton. It wasn't the Ukrainians. It was the Russians. And they're coming after us again. So to be concerned that the Russians are messing with presidential campaigns was a legitimate concern."

Why it matters: What was once a consensus due to the conclusions of the U.S. intelligence community has become something of a litmus test for loyalty toward President Trump, who has promoted allegations that Ukraine interfered in 2016 on behalf of Democrats.

Trump's request that Ukraine's president investigate whether the DNC's server is hidden in his country — a baseless conspiracy theory — contributed to the opening of the impeachment inquiry due to allegations that he withheld military aid until the investigation was announced.

Graham has been among the fiercest critics of the impeachment inquiry, but has declined to give credence to the idea that it was Ukraine, not Russia, that interfered in 2016.

The big picture: Graham used his opening statement to blast the FBI for the significant factual errors and omissions that officials made in surveillance applications for Trump campaign aide Carter Page.

The inspector general's report rebuked the FBI for its serious oversights but ultimately concluded that the Russia investigation was not tainted by political bias.

Go deeper: Read Inspector General Michael Horowitz's opening statement at FISA hearing