Donald Trump Jr jokes his favorite Democrat is 'Mitt Romney'
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Donald Trump Jr.Donald (Don) John TrumpTrump Jr., Meadows wear matching Trump jackets on 'Fox & Friends' Group auctioning off hunting trip with Donald Trump Jr. Trump allies to barnstorm Iowa for caucuses MORE joked in a recent interview that his "favorite Democrat" is Republican Sen. Mitt RomneyWillard (Mitt) Mitt RomneyProgressives hope Nevada offers roadmap for pro-union 2020 victory Texas woman sentenced for illegal voting faces deportation after parole Trump campaign buys top advertising spot on YouTube for Election Day MORE (Utah), a frequent critic of Trump Jr.'s father. 

Asked, "Who is your favorite Democrat?" by CBS host Gayle KingGayle KingGinsburg, accepting lifetime achievement award, urges working fathers to take an active role in kids' lives Gayle King accepts Snoop Dogg apology, says it was never her intention to add to pain over Bryant's death Snoop Dogg apologizes to Gayle King in Kobe Bryant flap: I was 'disrespectful' and 'overreacted' 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 TrumpComey responds to Trump with Mariah Carey gif: 'Why are you so obsessed with me?' Congress to get election security briefing next month amid Intel drama New York man accused of making death threats against Schumer, Schiff MORE, particularly after revelations that the president pushed Ukraine's leader to investigate Democratic presidential candidate Joe BidenJoe BidenPoll: Bloomberg stalls after Vegas debate Bloomberg campaign: Vandalism at Tennessee office 'echoes language from the Sanders campaign and its supporters' Democratic strategist says Biden 'has to' get second place in Nevada 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.