Watch live: Former Deputy AG Yates calls Flynn case dismissal 'highly irregular'

Aug. 5 (UPI) -- Former Deputy Attorney General Sally Yates described the Justice Department's decision to drop its case against former national security adviser Michael Flynn as "highly irregular" during her appearance Wednesday before the Senate.

She made the comment during a hearing of the Senate judiciary committee as part of its investigation into the origins of former special counsel Robert Mueller's Russia investigation.

Flynn pleaded guilty to lying to the FBI about conversations he had with former Russian Ambassador Sergey Kislyak. He later withdrew the plea and Attorney General William Barr moved to dismiss the criminal case.

Yates said that Justice Department decision was "highly irregular" and stood by her office's decision to investigate Flynn in late 2016 for allegedly attempting to undermine the Obama administration's sanctions on Russia when he spoke to Kislyak.

"If Gen. Flynn didn't think he was doing anything problematic, then he wouldn't have needed to do anything to cover it," Yates told the panel.

Flynn told Vice President Mike Pence and the FBI that he didn't encourage Kislyak to ask the Russian government not to retaliate against the Obama-era sanctions since Trump would be taking office after the new year.

NPR reported that documents later proved that Flynn, in fact, did speak to Kislyak about the issue.

Committee Chairman Lindsey Graham, R-S.C., accused the Obama-era Justice Department of targeting Flynn because of politics.

"The only problem here is that you didn't like Flynn changing the policy or talking about changing the policy," Graham said. "We're criminalizing policy differences. That's why Flynn got prosecuted because they hated his guts."

Yates was ultimately fired as acting attorney general by President Donald Trump.

The hear is part of Graham's efforts to investigate the origins of "Crossfire Hurricane," the name given by the FBI to its probe into possible connections between Russia and Trump's campaign during the 2016 election.

So far, Graham's investigation has focused on FBI surveillance of former Trump campaign adviser Carter Page and Flynn, as well as the use of the Foreign Intelligence Surveillance Act courts.

The last Crossfire Hurricane oversight hearing was held in June when former Deputy Attorney General Rod Rosenstein told the panel he would not have renewed a warrant for surveillance of Carter if he'd known there were questions about the FBI's handling of documents in the case.

Eight days later, the panel's Republican members voted to authorize 53 subpoenas in connection with the inquiry.

Democrats argue the hearings are a fishing expedition for dirt against Trump's political enemies before the 2020 election, and fear it could serve as a platform for spreading Russian misinformation.