Senator Ben Sasse, a conservative Republican Senator from Nebraska, says he will not support Trump in a general election. Instead, Sasse says he will vote for a third candidate, “a conservative option, a Constitutionalist.”

In a long letter to Trump supporters posted on his Facebook page, Sasse laid out the case against Trump. He points out that he himself is not an “establishment Republican,” and in fact was elected over the objections of the establishment, so Trump’s outsider status is not the reason he dislikes him. “Mr. Trump’s relentless focus is on dividing Americans, and on tearing down rather than building back up this glorious nation,” Sasse writes.

He also says Trump doesn’t understand our system of checks and balances that guards our liberty, thinking the President can run roughshod over the other branches of government. Sasse lists some Trump statements to illustrate and asks, “Which of the following quotes give you great comfort that he’s in love with the First Amendment, that he is committed to defending the Constitution, that he believes in executive restraint, that he understands servant leadership?”

Some of Trump’s statements Sasse listed include saying Putin is a great leader, saying he intends to use executive orders to get around Congress just like Obama did, saying he’s open to closing parts of the internet, threatening multiple lawsuits against opponents, and this gem of a Trump comment praising the dictatorial and oppressive Chinese government: “When the students poured into Tiananmen Square, the Chinese government almost blew it. They were vicious, they were horrible, but they put it down with strength. That shows you the power of strength.”

Most disturbing to longtime William F. Buckley, Jr., fans who come from the conservative base, was Trump’s remark that the editor of National Review, Rich Lowry, “should not be allowed on TV and the FCC should fine him.” Lowry had made a crude remark on Fox News about Carly Fiorina defeating Trump during one of the debates.

Republicans are split on whether to support Trump if he wins the nomination. There is a legitimate fear that if enough Republicans desert him in the general, it will enable liberal Hillary Clinton to win the presidency. Other prominent Republicans who refuse to support Trump in the general include former Oklahoma Congressman J.C. Watts, former New Jersey Governor Christine Todd Whitman, and former Florida congressman and RNC chair Mel Martinez.

On the other hand, Speaker Paul Ryan has been critical of Trump but says he will support him in the general.  New Jersey Governor Chris Christie, who attacked Trump relentlessly during the debates and is considered an establishment Republican, surprised everyone when he endorsed Trump after dropping out of the race. Popular talk show host Hugh Hewitt, who has no love for Trump, said it is imperative to support Trump if he wins the nomination because of the importance of appointing conservative Supreme Court justices (even though there are reasons to doubt whether Trump will appoint conservative justices).

It remains to be seen whether Republicans desert Trump en masse or embrace him. News outlets are referring to the dilemma as the Republicans’ civil war. If Trump secures the nomination, will Republicans who dislike him hold their noses and vote for Trump in the general — which may not even work since Trump is losing to Clinton and Sanders in most general election polls? Or will they support a third-party candidate who has little chance of winning, throwing the race to the Democrats in the general?

A third option for those like Sasse who see Trump as a dangerous threat to liberty and conservatism, assuming Trump remains the frontrunner in the GOP race but fails to get a majority of the GOP delegates: an open convention where the GOP replaces Trump with another standard-bearer. That strategy, of course, might still create a third-party run, but in this case, with Trump as the third-party candidate. That, too, could throw the general election to the Democrats.

Follow Rachel on Twitter at Rach_IC.