Donald Trump Jr jokes his favorite Democrat is 'Mitt Romney'
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Donald Trump Jr.Donald (Don) John TrumpResistance or unhinged behavior? Partisan hatred reaches Trump's family George Conway and Trump Jr. trade personal insults during impeachment hearing Trump: 'Everybody knows who the whistleblower is' MORE joked in a recent interview that his "favorite Democrat" is Republican Sen. Mitt RomneyWillard (Mitt) Mitt RomneyDeval Patrick: a short runway, but potential to get airborne Ocasio-Cortez jabs 'plutocratic' late entrants to 2020 field Jon Huntsman expected to run for governor in Utah MORE (Utah), a frequent critic of Trump Jr.'s father. 

Asked, "Who is your favorite Democrat?" by CBS host Gayle KingGayle KingTrump Jr's 'Triggered' debuts at No. 1 on NY Times bestseller list Donald Trump Jr jokes his favorite Democrat is 'Mitt Romney' Bruce Springsteen: Trump 'doesn't have a grasp' on what being American means MORE, the president's son quipped, "Mitt Romney, Gayle. Mitt Romney's my favorite Democrat."

Romney, the 2012 Republican presidential nominee, has often criticized President TrumpDonald John TrumpGOP divided over impeachment trial strategy Official testifies that Bolton had 'one-on-one meeting' with Trump over Ukraine aid Louisiana governor wins re-election MORE, particularly after revelations that the president pushed Ukraine's leader to investigate Democratic presidential candidate Joe BidenJoe BidenBudget official says he didn't know why military aid was delayed: report Growing 2020 field underscores Democratic divide READ: Foreign service officer Jennifer Williams' closed-door testimony from the House impeachment inquiry MORE and his son. 

Romney called a transcript released by the White House of the president's phone call with Ukrainian President Volodymyr Zelensky "deeply troubling."

The revelation that Trump pushed for the probe into the Bidens is at the center of a House impeachment inquiry. 

The president has denied wrongdoing and has publicly asked Ukraine and China to investigate the former vice president. Romney also called this move "wrong and appalling."

Trump in a tweet last month called Romney "pompous."

Trump Jr.'s book, "Triggered: How the Left Thrives on Hate and Wants to Silence Us," was released on Tuesday and already sits on the Amazon bestsellers list.

— Joe Concha contributed to this report, which was updated at 10:24 a.m.