Colorado Congressman Mike Coffman became the first House Republican on Thursday to take on Donald Trump in an advertisement for his own re-election campaign, promising to "stand up" to the GOP presidential nominee between if he makes it to the White House.

Coffman, a Iraq war veteran, plans to run the 30-second ad in Colorado beginning on Friday. He will also release a version of the commercial in Spanish to target Hispanics who make up 20 percent of his voting district.

"People ask me, 'What do you think about Trump?'" Coffman says in the ad. "Honestly, I don't care for him much."

"I'm a Marine. For me, country comes first. My duty is always to you. So if Donald Trump is the president, I'll stand up to him. Plain and simple," he continues.

The new ad marks a significant step for incumbent Republicans who have sought to distance themselves from Trump, who faces record low favorability ratings among GOP voters in battleground states like Colorado. Because of his unpopularity, many down-ballot Republicans believe embracing Trump could jeopardize their own campaigns.

An adviser to Coffman told Politico that the candidate hopes to capitalize on voter frustration with Trump through the release of his new ad.

"Mike has been persistently critical of Trump," said Josh Penry. Assuring voters that he would stand up to a President Trump if need be "was the right thing [for Coffman] to do. It's on people's' mind," he added.

Coffman has not endorsed Trump and is still deciding whom to support in the presidential race. In the same ad, however, the Colorado Republican said he "certainly" doesn't trust Hillary Clinton and would "hold her accountable every step of the way" if she defeats Trump in November.