At a May 12 fundraiser at the Elbert County Fairgrounds, Coffman wrapped up a 12-minute speech to donors with an unprompted discussion of President Obama's citizenship and national identification.
Listen to the full audio from the event. The comment about President Obama is made at 11:30.
"I don't know whether Barack Obama was born in the United States of America. I don't know that," Coffman said. "But I do know this, that in his heart, he's not an American. He's just not an American."
After a short pause, which Elbert County Republican Chairman Scott Wills recalled as "deafening silence," Coffman was met with applause, tentative at first.
The recording and a photo of the event were posted online by Coffman supporter Brooks Imperial, who attended the fundraiser.
"I'm glad the congressman said it. Not enough have. More should," Imperial said.
9NEWS was informed ofImperial's postingby the Democratic Congressional Campaign Committee.
Coffman issued a written apology Wednesday evening.
"I misspoke and I apologize," the statement began. "I have confidence in President Obama's citizenship and legitimacy as President of the United States."
Coffman went on to offer a defense of his intent.
"I don't believe the president shares my belief in American Exceptionalism. His policies reflect a philosophy that America is but one nation among many equals," the statement read. "As a Marine, I believe America is unique and based on a core set of principles that make it superior to other nations."
9NEWS Political Analyst Floyd Ciruli, a pollster, says Coffman's comment is a blow to his moderate image.
"Radical statements about the president, where his heart is, whether he's an American, are going to be tremendously controversial," Ciruli said.
Coffman's 6th Congressional District has been redrawn to include fewer Republicans, a point Coffman acknowledged at the May 12 fundraiser.
"It is going to be a very challenging race," Coffman is heard saying. "I really need your help."
Ciruli says Coffman's line may have gone over well in "red" Elbert County, but he'll need to do well with moderate voters in "purple" Arapahoe County.
"That may have gotten a hand out there but in the Denver metro area, those are very extreme comments," Ciruli said. "I think they will probably give the Democrats a little fodder for some ads."
A spokesman for Coffman's Democratic challenger, State Rep. Joe Miklosi (D-Aurora), weighed in with a statement painting Coffman as out of the mainstream.
"These outrageous comments once again make clear that Mike Coffman is Colorado's version of Rush Limbaugh," Miklosi spokesman Joe Hamill said. "This kind of extremism is why Washington doesn't work."
"We need leaders who will work together for solutions, not join the far right birther fringe or attack the President of the United States as un-American," Hamill said.
The fundraiser in Elbert County was hosted for Coffman by fellow Republican Congressman Cory Gardner.
9NEWS asked Gardner if he agreed with Coffman's comments about the president.
In a written statement, Gardner said, "Congressman Coffman is a leader and a patriot that has served his country his entire life. I know for a fact he does not question the legitimacy of President Obama's birth certificate."
Gardner's staff later clarified that he also accepts President Obama's eligibility and birth certificate.