Biden, after the first presidential debate against the former president, demonstrated that he is not electable and cannot win the presidential election in November, Gilmore said.
"I think that President Trump got everything across, and naturally, he demonstrated complete mental acuity," Gilmore added.
Gilmore pointed out that Trump successfully discussed African American voters and the inflation problem in the United States, and addressed the Biden administration's chaotic withdrawal from Afghanistan.
"I thought that President Biden came across a sort of angry old man and a lot of vulgarity, which kind of took me aback," Gilmore said.
Numerous Democrats have reportedly expressed concerns about Biden's poor performance and its implications for the future of his candidacy and are even talking about potential candidates who can replace him in the presidential race.
"I believe he's not electable," Gilmore said Thursday night. "I think the Democrats in the United States have a problem. And I think they've got a candidate who probably can't win."
Gilmore added that he was shocked Democrats believe Biden should step aside, but he expects the incumbent president will continue his run in the presidential race.
Trump and Biden are set to debate again on September 10 in an ABC-moderated event.