"In a way, because the president is defying these traditions of not being part of the inauguration of President-elect Joe Biden, he's almost leaving town like an autocrat, ousted from power, heading off into exile," Acosta said at Joint Base Andrews, shortly before Trump arrived to give a final address as president.
Acosta, who is leaving his White House beat as Biden takes office, said it could end up being "one of the smallest Trump rallies."
"For a president who is obsessed with crowd sizes, this may not be to his liking when he gets over here," Acosta said.
CNN anchor Wolf Blitzer called the crowd for Trump's departure "pathetic."
Trump flew to Florida with family members on the final day of his presidency.
Acosta's editorializing was a fitting end for a correspondent who constantly meshed journalism and advocacy, heavy on melodrama but light on scoops. It led to praise from some liberal corners and the "Resistance," but even some of his own White House colleagues expressed discomfort at his bombastic coverage.
Acosta's disdain for Trump was mutual; Trump called him a "terrible person" in one infamous exchange in 2018.
Trump later addressed the crowd and thanked his family and friends for support, touted administration accomplishments, and wished the next president well, although he did not name him. Trump came under fierce criticism from both sides of the aisle for never formally conceding the 2020 election, and he is the first sitting president to skip a successor's inauguration since Andrew Johnson in 1869.