Donald Trump Jr. Don John Trump'Tiger King' star Joe Exotic requests pardon from Trump: 'Be my hero please' Zaid Jilani discusses Trump's move to cancel racial sensitivity training at federal agencies Trump International Hotel in Vancouver closes permanently MORE slammed Roy Moore Roy Stewart MooreRoy Moore sues Alabama over COVID-19 restrictions Vulnerable Senate Democrat urges unity: 'Not about what side of the aisle we're on' Sessions hits back at Trump days ahead of Alabama Senate runoff MORE’s (R) decision on Thursday to run for Senate in Alabama, saying that the former Alabama Supreme Court justice is “doing a disservice to all conservatives” by running.

“I can assure everyone that by running, Roy Moore is going against my father and he’s doing a disservice to all conservatives across the country in the process,” the president's eldest son wrote in a Thursday afternoon tweet.

This is pure fake news. I can assure everyone that by running, Roy Moore is going against my father and he’s doing a disservice to all conservatives across the country in the process. https://t.co/pjfDKfoIO0 — Donald Trump Jr. (@DonaldJTrumpJr) June 20, 2019

Trump Jr.'s comments come after Moore announced earlier Thursday that he would run for Senate in Alabama again, challenging incumbent Sen. Doug Jones (D-Ala.) for his seat in 2020 after losing to him in a contentious special election in 2017.

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President Trump Donald John TrumpSteele Dossier sub-source was subject of FBI counterintelligence probe Pelosi slams Trump executive order on pre-existing conditions: It 'isn't worth the paper it's signed on' Trump 'no longer angry' at Romney because of Supreme Court stance MORE first weighed in on Moore’s candidacy last month, saying Republicans "cannot allow themselves to again lose the Senate seat in the Great State of Alabama.” He added at the time that he didn't think Moore could win.

Moore on Thursday said his decision to run is “not going against” Trump, but Trump Jr. made clear that the president does not support his campaign.

The president first threw his support behind Moore during his 2017 run to replace Jeff Sessions Jefferson (Jeff) Beauregard SessionsRoy Moore sues Alabama over COVID-19 restrictions GOP set to release controversial Biden report Trump's policies on refugees are as simple as ABCs MORE (R) in the Senate, despite allegations that the former judge pursued sexual and romantic relationships with teenage girls in the 1970s when he was in his 30s. Moore has denied the allegations against him.

Moore’s loss to Jones in 2017 gave Democrats their first Senate seat in Alabama in 25 years.

Before Moore wins a rematch against Jones, he will have to defeat former Auburn University football coach Tommy Tuberville, Rep. Bradley Byrne Bradley Roberts ByrneBottom line Jerry Carl wins GOP Alabama runoff to replace Rep. Bradley Byrne Jeff Sessions loses comeback bid in Alabama runoff MORE (R-Ala.) and state Rep. Arnold Mooney, who have all already declared their candidacy for the Republican nomination.