Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE on Wednesday sharply attacked a witness in the House's impeachment inquiry into his father, President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE, accusing Lt. Col. Alexander Vindman of being a "leftist" who Democrats have tried to portray as "beyond reproach."

In an interview with "Fox & Friends" on Wednesday morning, the president's eldest son lashed out at Vindman, a Purple Heart recipient and Iraq War veteran, accusing him without evidence of harboring left-wing political views.

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“They do the usual thing, they bring in another guy that they believe is beyond reproach. Like they did with Mueller,” Trump Jr. said, referring to former special counsel Robert Mueller Robert (Bob) MuellerCNN's Toobin warns McCabe is in 'perilous condition' with emboldened Trump CNN anchor rips Trump over Stone while evoking Clinton-Lynch tarmac meeting The Hill's 12:30 Report: New Hampshire fallout MORE, another decorated veteran who served in the Vietnam War.

“It was a joke. So now they’ll do it with this guy. …Now it turns out he’s talking to the Ukraine or he wanted to edit [the] transcript," Trump Jr. continued.

He added later: “You only get total absolution if you are a leftist veteran. Not a veteran, just a leftist. If you’re on their side, you can do no wrong.”

Fox News host Brian Kilmeade cut in, reminding Trump Jr.: “But we don’t know if he’s a leftist."

“Oh yeah, of course. Sure," Trump Jr. responded.

The remarks represented the latest round of attacks from allies of President Trump against witnesses in House Democrats' impeachment inquiry.

Vindman serves as the top Ukraine expert on the White House National Security Council, though the president himself has sought to dismiss him the past two days, calling him a "Never Trumper" on Twitter.

Allies of the president have also questioned on cable shows whether the U.S. Army veteran was secretly loyal to his home country of Ukraine, which he left at age 3.

Several Republicans lawmakers have forcefully pushed back on attempts to question the U.S. official's intentions or attempt to discredit him.

Vindman told House investigators on Tuesday that parts of a readout of Trump's call with Ukraine's president, which has become the center of Democrats' impeachment investigation, was edited to remove key phrases from the conversation.

The first official who witnessed the call first hand to testify as part of the impeachment inquiry, Vindman told lawmakers he was troubled by Trump urging the Ukrainian president to investigate a political rival and said he reported it to his supervisor.