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Sen. Ben Sasse, R-Neb., speaks during the annual Conservative Political Action Conference (CPAC) 2016 at National Harbor in Oxon Hill, Maryland, on March 3. Getty Images

United States Sen. Ben Sasse, R-Neb., penned an open letter on Facebook Wednesday night criticizing presidential front-runners Donald Trump and Hillary Clinton and encouraging voters to find an honest, mature leader. Sasse, who's been in office since January 2015, labeled Trump and Clinton "terrible options," pushing instead for a candidate who isn't part of the establishment, promises to only serve one term and hopes to move the country forward.

"There is no reason to believe that either of these two national front-runners believe in limiting anything about D.C.’s power," Sasse wrote. "I believe that most Americans can still be for limited government again — if they were given a winsome candidate who wanted Washington to focus on a small number of really important, urgent things — in a way that tried to bring people together instead of driving us apart. I think there is room — an appetite — for such a candidate."

Politico noted Sasse was quick to disqualify himself, adding that the would-be candidate needs to have a schedule that allows him or her to campaign constantly until November, a stipulation that would exclude parents of young kids. Sasse has three children.

Sasse also vowed to continue to fight for the Republican party, but he said neither the GOP nor Democratic party were working well. They were spending too much time "bicker[ing] like children about tiny things," which has alienated voters — young voters, in particular — he added.

Despite being their respective parties' leaders, both Trump and Clinton have negative ratings, according to RealClearPolitics data. Trump, who has 1,053 delegates of the 1,237 needed to secure the GOP nomination, has a net favorable rating of -37. Clinton, who has 2,205 of the 2,383 delegates needed for the Democratic gig, has a net favorable rating of -16.5.

"With Clinton and Trump, the fix is in. Heads, they win; tails, you lose," Sasse wrote. "Why are we confined to these two terrible options? This is America. If both choices stink, we reject them and go bigger. That’s what we do."

Wednesday wasn't Sasse's first foray into the presidential debate. The senator previously aligned himself with the #NeverTrump movement, a group of Republicans who have broken with the party to say they will not back Trump should he win the nomination, the Hill reported. Sasse voted for Sen. Ted Cruz, R-Texas, in the Nebraska primary last month, but Cruz dropped out of the race Tuesday. Ohio Gov. John Kasich suspended his campaign Wednesday, leaving Trump the presumptive nominee.

There are a few third-party hopefuls campaigning for the Oval Office already, among them the Green Party's Jill Stein and Libertarian Gary Johnson, according to NBC News. Third-party candidates primarily serve to influence political discussion, though they can have an impact on the general election: In 1992, independent Ross Perot received nearly 19 percent of all votes.

"Minor parties have been working and working and working all these years, and it's slowly paying off," Richard Winger, publisher of Ballot Access News, told USA Today last month. "Nobody notices because it's little incremental changes, but it's adding up."

Read Sasse's full letter below: