Story highlights Kinzinger said Wednesday he "doesn't see how" he can endorse Trump

He said he's contemplating writing in a candidate

Washington (CNN) Republican Rep. Adam Kinzinger said Wednesday that he doesn't see how he can endorse his party's nominee, Donald Trump, in the wake of the week's events.

"I'm an American before I'm a Republican," he told CNN's Wolf Blitzer on "The Situation Room." "I'm saying for me personally, how can I support that? Because he's crossed so many red lines that a commander in chief or a candidate for commander in chief should never cross."

Kinzinger, who has openly hesitated to embrace Trump as his party's standard-bearer, said he went to Cleveland hoping to "at least mildly endorse the Republican front-runner."

But in the aftermath of Trump's comments about Russian President Vladimir Putin and the parents of fallen Muslim American soldier Capt. Humayun Khan, the third-term Illinois congressman said that he doesn't "see how I get there anymore."

"I'm a Republican because I believe that Republicanism is the best way to defend the United States of America," Kinzinger said, adding that Trump "throws all of these Republican principles on their head."

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