Former Pennsylvania Republican Rep. Charlie Dent defended his frequent criticism of President Donald Trump on Wednesday, and added a dig at his former GOP colleagues who won’t do the same.

“People ask me: Why do I push back against this administration and the president?” Dent said on CNN. “Because my nose is not a heat-seeking missile for the President’s backside, and people have to stand up and say, and talk clearly, to the American people."

Dent’s remarks came as House Democrats’ impeachment inquiry into Trump gains steam. William Taylor Jr., Trump’s top diplomat in Ukraine, told impeachment investigators on Tuesday that Trump clearly tied aid for Ukraine to a demand for the country to investigate Trump’s political rivals.

“This is wrong,” Dent said Wednesday. "You cannot use your official resources, official resources of the government, to investigate your political opponent.”

Dent, a moderate who represented the Lehigh Valley from 2005 to 2018, was a rare Trump critic among House Republicans before joining a wave of lawmakers who retired rather than face reelection amidst an anti-Trump wave in the midterm elections.

Dent’s remark that his nose is "not a heat-seeking missile for the President’s backside,” which quickly shot across Twitter, echoed a quote in a recent New Yorker article about Secretary of State Mike Pompeo, in which a former American ambassador described Pompeo as “a heat-seeking missile for Trump’s ass.”

“I don’t know how any Republican member can look at this thing, or any member of Congress, and not be alarmed by this," Dent said. "I mean, the quid pro quo was stark. And the [president] is insisting on using official resources to dig up dirt on his opponent. I mean, this is simply indefensible.”

On Tuesday afternoon, Dent joined the Twitter spree set off by his remarks, posting a GIF showing a toy rocket hitting a man in the rear.

Dent sparred with fellow former Republican Rep. Sean Duffy of Wisconsin, who attempted to cast doubt on the inquiry and argued there was no quid pro quo with Ukrainian leaders. His voice increasingly strained, Dent shot back the line about the heat-seeking missile, saying the president’s behavior was stunning.

“It is non-persuasive to me,” Duffy said of Taylor’s testimony on Tuesday. He also criticized Democrats for holding private hearings in the impeachment inquiry.

Trump has denied any wrongdoing.

“I was the chairman of the Ethics Committee," Dent said. "If a member of Congress had done anything like this, they would’ve been investigated, they would’ve been referred to the Department of Justice. End of story.”