"I'm the only veteran ... in this race," Gilmore said at Thursday night's undercard debate in Iowa. "And I'm not going to any Donald Trump event over across town on some sort of faux veterans sort of issue.
"I'm going to speak to you tonight about the issue that really confronts veterans. I'm going to talk to you about the concerns they have with the Veterans Administration, the lousy appeals process that they've got, the fact sometimes they get good service at the VA."
Trump decided to boycott Thursday's night primetime debate amid a feud with Fox News and anchor Megyn Kelly. He will instead hold an event scheduled at the same time as the debate, with the proceeds going to veterans groups.
Fellow GOP candidates Mike Huckabee and Rick Santorum both said earlier that they'd attend Trump's event after the undercard debate. Both of them shared the stage with Gilmore at the undercard debate.
Gilmore, who has barely registered in the polls, has barely campaigned in Iowa and said that he's putting his focus on New Hampshire.