Former White House Homeland Security Advisor Tom Bossert said on Sunday that he’s “deeply frustrated” how Rudy Giuliani and the rest of President Donald Trump’s legal team keep pushing the DNC server hack conspiracy theory.

The White House’s explosive memo on Trump’s call with Ukrainian President Volodymyr Zelensky revealed that Trump not only pressured Zelensky to investigate 2020 rival Joe Biden, but also look into the conspiracy theory that Ukraine, not Russia, had hacked the DNC server and gotten ahold of Hillary Clinton’s emails in 2016.

“It’s not only a conspiracy, it is completely debunked,” Bossert told ABC News’ “This Week” host George Stephanopoulos.

The former homeland security advisor said he was “deeply frustrated with what [Giuliani] and the legal team is doing and repeating that debunked theory to the President.”

“It sticks in his mind when he hears it over and over again and for clarity here, George, let me just again repeat that it has no validity,” Bossert added. “The United States government reached its conclusion on attributing to Russia the DNC hack in 2016 before it even communicated it to the FBI, long before the FBI ever knocked on the door at the DNC.”

Watch Bossert below: