Trump Jr. retweeted conspiratorial remarks by white supremacist Kevin B. MacDonald about alleged favors exchanged by Hillary Clinton and Switzerland's largest bank. On the campaign trail, Trump Jr. promoted Alex Jones' conspiracy theory that Hillary Clinton wore an earpiece to a presidential forum and that official unemployment rates were manipulated for political purposes.
In May 2017, Trump Jr. promoted what CNN called the "long-debunked, far-right conspiracy theory" that Bill Clinton was linked to Vince Foster's death. In November, Trump Jr. again promoted the conspiracy theory that the Clintons had murdered people.
In February 2018, Trump Jr. liked two tweets promoting a conspiracy theory that survivors of the Stoneman Douglas High School shooting were coached into propagating anti-Trump rhetoric.
In May 2018, Trump Jr. retweeted a false and antisemitic conspiracy theory that George Soros, the Jewish Hungarian-American businessman and philanthropist, was a "nazi [sic] who turned in his fellow Jews to be murdered in German concentration camps & stole their wealth". The tweets originated from Roseanne Barr, whose TV show Roseanne was canceled the same day after she had posted a series of racist and antisemitic tweets. A spokesperson for Soros responded to the tweets, "George Soros survived the Nazi occupation of Hungary as a 13-year-old child by going into hiding and assuming a false identity with the help of his father, who managed to save his own family and help many other Jews survive the Holocaust".
In June 2018, Trump Jr. liked a tweet suggesting that the migrant children separated from their parents due to the Trump administration family separation policy were actually actors.
In September 2018, when Hurricane Florence was affecting the United States, Trump Jr. tweeted a picture of CNN journalist Anderson Cooper waist-deep in floodwaters when another man in the same picture was standing knee-deep a distance away. In the same tweet, Trump Jr. included a link to a Breitbart News article claiming that CNN's ratings had dropped by 41%, and proposed a conspiracy theory that CNN was "lying to try to make [his father, President Trump] look bad". In actuality, the picture of Cooper was about 10 years old, taken during 2008's Hurricane Ike before Trump became president, and Cooper was videoed talking about how the floodwaters were receding.
In May 2020, Trump Jr. falsely accused Joe Biden of being a pedophile. After Biden was diagnosed with prostate cancer in May 2025, Trump Jr. launched a conspiracy theory questioning how Jill Biden, who received a doctoral degree, missed the signs and whether it was covered up. Trump Jr.'s response was seen as an outlier compared to other politicians including his father's, and was a subject of criticism. However, he had also liked a post wishing Biden a speedy recovery, "politics aside."
In August 2020, Trump Jr. shared a Breitbart News article about more than 800 dead people voting in Michigan which was framed to suggest that the ballots were not legitimately cast and thus showed evidence of extensive voter fraud; however, the voters in question died after submitting the ballots, and the ballots were rejected by Michigan authorities who knew the voters had died before the election date. In September 2020, he again pushed false claims about voter fraud by asserting, "The radical left are laying the groundwork to steal this election from my father". He added: "Their plan is to add millions of fraudulent ballots that can cancel your vote and overturn the election" and asked "able-bodied" people to join an election security "army" for his father. Facebook and Twitter affixed labels to the video which pointed to accurate information about voting.
In November 2020, after Pfizer announced that it had developed a COVID-19 vaccine with 90% effectiveness, Trump Jr. suggested that the vaccine had been held back in order to hurt his father's chances of winning the election. Pfizer CEO Albert Bourla dismissed the suggestion, saying that the company had always planned to rely on the "speed of science".
After Russia invaded Ukraine in February 2022, Trump Jr. amplified baseless Russian state propaganda which claimed that the US and Ukraine were developing biological weapons.
