Rep. Adam Kinzinger has long been skeptical of Donald Trump, but said that he "wanted to get" to a place where he could feel comfortable endorsing the GOP nominee.

But, as the Illinois congressman and Air Force pilot told Wolf Blitzer Wednesday evening, that window of support appears to be closed, saying "I don't see how I can get there anymore."

Among "other sins," Kinzinger cited Trump's comments on NATO, his attacks on a gold star family, "blaming George Bush for 9/11" as "red lines of the unforgivable in politics" that Trump was crossing. "I'm an American before I'm Republican," he said.

Watch the interview below.