I am a registered Republican.

It is an honor to belong to the Party of Lincoln. I am proud to support the party that has consistently and strongly advocated for the State of Israel, despite a remarkable lack of reciprocation by Jewish voters. I find in the Republican party a reflection of my values and responsiveness to my concerns in matters of policy, both foreign and domestic. I was happy to support Chris Christie in the 2013 gubernatorial election, soon after becoming a citizen of the Garden State.

One of my proudest moments as an American was a brief introduction to the late Supreme Court Justice Antonin Scalia, whose intellect dazzled me and whose recent death deeply saddened me. I was reminded by the justice’s passing of a much earlier trip to Washington, where I joined grateful throngs to witness the funeral cortege of President Ronald Reagan. I was genuinely moved by the imposing military flyover, and by the sight of the riderless horse, with boots turned backward in its stirrups, as is customary at presidential funerals.

Never before, however, have I more painfully felt the prospect of riderlessness in American governance, nor witnessed more backward thinking among the American electorate, than with the political ascendancy of Donald Trump.

And never before have I felt more painfully or more personally disappointed in a politician than I was by Governor Chris Christie when he endorsed the real estate mogul.

To be sure, many elected officials have committed far more egregious betrayals of the public trust, breaches of common decency, and in some cases criminal acts. The governor’s endorsement left me personally aghast, however, as it is so very at odds with the esteem in which I heretofore had held him.

Mr. Trump is a bully. I am convinced that he lacks the character, the moral compass, the temperament, the experience, and the judgment we should demand in a president. He is a narcissist and a demagogue, whose true gifts are a penchant for self-promotion and name-calling. He has belittled his opponents, demeaned Amery can heroes, dishonored the pope, trafficked in ethnic stereotypes and racial innuendo, and further coarsened the already debased standards of political discourse.

Donald Trump rushes in where the better angels of our nature fear to tread. I do not wish further to debate or to expand upon Mr. Trump’s voluminous shortcomings, for I am convinced that his lack of suitability for the presidency, and with it the leadership of the free world, is — in terms borrowed from our founding fathers — a self-evident truth. That so many Americans fail to understand this is profoundly disheartening. It is frightening. It is a sign that not only is the American political system troubled, the American electorate is all but broken.

Why is Governor Christie among Donald Trump’s supporters? I want to believe he is too smart to be sincere in his support. Is he acting out of spite toward the other candidates who maligned him in the course of the campaign? Is he hoping for a vice-presidential nod from a former opponent whose nomination he now considers inevitable? Does he foresee that Mr. Trump’s limitations and failings make his early removal from office far from unlikely, rendering the vice presidency a temporary position with significant growth potential? Does he aspire to other high office in a Trump administration?

I long have believed Mr. Christie would be an excellent vice president or an outstanding attorney general. I have believed he would make a fine president. If, however, Governor Christie has leveraged his endorsement of a patently unfit candidate with the hope of advancing his own political fortunes, he has proven the wisdom of perennially unsuccessful presidential aspirant Adlai Stevenson: “The hardest thing about any political campaign is how to win without proving that you are unworthy of winning.”

I am disappointed, as well, in the field of Republican can dilates who have remained in the presidential race despite minimal support, knowing that they thereby were dividing the party vote and facilitating Mr. Trump’s lamentable rise. No leader who is unwilling to sacrifice personal political prospects in the service of his country is fit to be commander-in-chief, and of assuming the responsibility of sending young Americans to risk and to sacrifice their lives in the service of their country.

Donald Trump’s nomination never was — and still is not yet — inevitable. Recklessly self-serving politicians have conspired with a broken electorate, however, to make that nomination an increasingly real possibility.

Sacrificing personal advancement in order to assure selection of a worthy national leader — despite believing oneself deserving of that coveted position and capable of greatness — is precisely what gave the Jewish people one of its most celebrated and highly esteemed figures. B’nei Beteira, a dynastic family of rabbinic scholars, ceded the office of Nasi (head — literally, president — of the Sanhedrin) to Hillel, when Hillel’s superior erudition and scholarship became obvious. (See Pesachim66A.) Rather than cling to continued power or aspire to higher office, the self-sacrificing B’nei Beteira acted in the best interests of the nation — that is, of us — by stepping aside to assure selection of a worthy nasi, a president truly suited to that lofty station.

Rabbi Yehudah Ha-Nasi, redactor of the Mishnah, and as his title indicates a Sanhedrin president — was a rabbinic giant of such proportions that he is known merely as “Rabbi.” That is, he continues to be viewed as “the” rabbi, par excellence. Rabbi paid tribute to the humility and worthiness of B’nei Beteira.(See Baba Metzia 84B-85A.)He classified their self-sacrificing humility together only with that of his own sainted father, Rabban Shimon ben Gamliel, and Jonathan, the first prince of Israel, who died defending his nation on the field of battle.

Those who would lead our nation, those who would rebuild, deploy, and command our military in defense of the homeland and for the sake of humanity, must at the very least be capable of self-sacrificing courage. Though the hour is late, Republican candidates for president have a moral duty immediately to cede their own prospects for election so that one among them — a worthy opponent — can realize his full potential with a viable challenge to Donald Trump.

It is not my purpose here to name or to designate that candidate. But it is not too late to recognize that we need in the next leader of the free world — even as a civilizational struggle with radical Islam looms— quite a bit more than Donald Trump will ever have to offer.

There may not be a Hillel among the Republican candidates, nor among the Democrats. That would be asking a great deal indeed. I pray fervently, however, that there just might be a few B’nei Beteira.

I am a registered Republican. I am proud to belong to the Party of Lincoln. If Donald Trump becomes the GOP’s standard-bearer, however, I will not support the nominee of my party. That is true even if Chris Christie is on the ticket, as I had always hoped he would be.

To this I pledge my sacred honor.