Donald Trump Jr.'s Skittles Tweet Highlights His Key Campaign Role

The Republican candidate's eldest son is under fire.

— -- Using Skittles to make a point about "our Syrian refugee problem" didn't go over too well with Mars Inc., but the candy maker's rebuke of Donald Trump Jr.'s controversial tweet is hardly a first.

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.

He also didn't remove his Instagram post of Sept. 11, which was meant to be a play on Hillary Clinton's reference to some of his father's supporters as "a basket of deplorables."

That photo, which he wrote was sent to him by "a friend," replaced images from the movie "The Expendables" with pictures of Donald Trump Sr., alt-right conspiracy theorist Alex Jones, alt-right blogger Milo Yiannopolous and other well-known Trump supporters like Gov. Chris Christie, Dr. Ben Carson and political strategist Roger Stone.

It also included a cartoon frog named Pepe, which is regularly used by alt-right supporters.

Donald Trump Jr. has been actively involved in his father's campaign, in public and private.

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.

In May, Donald Trump Jr. met on his own with Republican officials and the National Rifle Association on Capitol Hill.

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.