The eldest Trump son posted a photo of a bowl of Skittles and a caption that reads, "If I had a bowl of skittles and I told you just three would kill you. Would you take a handful? That's our Syrian refugee problem."
The condemnation was swift, though he appears to be standing by the sentiment and has not removed the post.
It also included a cartoon frog named Pepe, which is regularly used by alt-right supporters.
He was the one to cast the convention floor vote for his father that put the Republican presidential candidate over the top and secured him the nomination. Of the three Trump children active in their father's campaign, Donald Trump Jr. was the first to give a speech at the party convention in Cleveland this summer — which was well received by many in the audience.
"Donald Trump Jr. was so excellent that my brain was already thinking, ‘What should we run him for?'" Trisha Turner, the president of the New York State Federation of Republican Women, told ABC News at the convention.
He has also played a significant role behind the scenes of his father's campaign.
Donald Trump Jr. was extensively involved in the vice presidential selection process, even meeting with V.P. hopeful Christie, along with his siblings Ivanka Trump and Eric Trump, without their father present.
A registered gun owner and known hunter, he was the one to lead the negotiations with the NRA leading up to the gun rights lobbying group's endorsement of his father, sources told ABC News.