Story highlights Republican Sen. Ben Sasse used social media Sunday to say he would not vote for Donald Trump

"I'm as frustrated and saddened as you are about what's happening to our country. But I cannot support Donald Trump," Sasse wrote

Washington (CNN) Republican Sen. Ben Sasse said Sunday he won't vote for Donald Trump if the billionaire and GOP presidential front-runner becomes his party's nominee.

"If Trump becomes the Republican nominee my expectation is that I'll look for some 3rd candidate -- a conservative option, a Constitutionalist," Sasse, a first-term senator from Nebraska, tweeted Sunday night.

If Trump becomes the Republican nominee my expectation is that I'll look for some 3rd candidate -- a conservative option, a Constitutionalist — Ben Sasse (@BenSasse) February 29, 2016

Sasse railed against Trump on social media, writing in one tweet that "The Presidency is not our national embodiment of Nietzschean Will."

He collected many of his concerns in a Facebook post

"I'm as frustrated and saddened as you are about what's happening to our country. But I cannot support Donald Trump," Sasse wrote. "Please understand: I'm not an establishment Republican, and I will never support Hillary Clinton. I'm a movement conservative who was elected over the objections of the GOP establishment. My current answer for who I would support in a hypothetical matchup between Mr. Trump and Mrs. Clinton is: Neither of them."

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