Billionaire Bill Ackman "formally" endorsed President Trump after an assassination attempt in Pennsylvania on Saturday.
More than 19 million people viewed Ackman's endorsement post late Saturday night.
"I came to this decision some time ago," Ackman said. "Many @X followers already understood from my supportive posts of Trump and my criticisms of @POTUS Biden." He added, "The reason I have not formally done so is that I want to explain my thinking in detail."
Ackman, CEO of Pershing Square Capital Management, said a "long-form post" is needed to explain his thinking. He hadn't found the time or urgency to write it before the shooting. The incident at a Trump rally injured Trump's ear, left one rally attendee dead, and two spectators critically injured.
Ackman believes the upcoming presidential election is "one of the most consequential" in his lifetime. He has spent hours with Trump recently. He urged voters to "keep an open mind." A detailed post explaining his position will come later.
In January, Ackman said President Biden was unfit to serve and called on him to step aside during a CNBC "Squawkbox" interview.
Billionaire Elon Musk also announced he "fully supports" Trump shortly after the shots rang out in Butler, Pennsylvania.
"All of us have an obligation to stand up and be counted," Ackman said in a subsequent X post on Sunday.