For those of us with a certain political bent and background, this is the most depressing moment of all. The best of the GOP — Marco Rubio and Paul Ryan, the intellectually serious reformicons who have called attention to issues of poverty and the need for Republican outreach — are bending their knee to the worst nominee in their party’s history. Ryan drags himself slowly. Rubio eventually went with a quick Band-Aid pull. But the largest political choice each man has made this year will be one of the worst mistakes of their careers.

How do I know this? It doesn’t require fortune-telling. Just days before Rubio offered to speak on Trump’s behalf at the Republican convention, the presumptive nominee declared the 1993 suicide of Vince Foster to be “very fishy,” especially given Foster’s “intimate knowledge of what was going on” with the Clintons. And Trump attacked the Republican governor of New Mexico, Susana Martinez, for allowing Syrian refugees to be “relocated in large numbers” to her state. “If I was governor,” he said, “that wouldn’t be happening.”

This is Trump on his best behavior, trying (once again) to act “presidential.” A previous column I wrote — examining Trump’s penchant for conspiracy thinking on issues from vaccination to the death of Antonin Scalia — appeared on the same day as Trump’s implication of Hillary Clinton in Foster’s death. One challenge of detailing Trump’s lunacy is the need for hourly updates. His allegation in the Foster case involved the exploitation of a personal tragedy, amounting to the mockery of a family’s loss. It revealed a wide streak of cruelty.

The attack on Martinez demonstrated another less-than-desirable leadership quality. Trump’s charge against her had nothing to do with refugee policy. During her time as governor, just 10 Syrian refugees have been relocated to New Mexico. Trump was attempting to punish Martinez because she has been noncommittal about endorsing him. In making judgments about people, Trump’s primary measure is not ideological or even political. He likes people who support him and disdains people who don’t. So Martinez and liberal Sen. Elizabeth Warren (Mass.) are lumped in the same category of lèse-majesté. It doesn’t matter that Martinez is known as an effective Republican governor. Trump demands the unity of adulation. He is incapable of magnanimity.

And this meanness of spirit is also applied to some of the most vulnerable people in the world. Trump’s mention of refugees was a subterfuge, but still a damaging one. To score his political point, Trump chose to heap disdain on a few people — vetted for years before arrival — who seek the protection of the United States after a terrible ordeal. Can you imagine, say, Ronald Reagan attacking women and children fleeing violence and oppression? They would more likely be used as an inspiring speech illustration. For Trump, the bully, a trickle of refugees is another chance to kick the weak.

Speaking at a rally in Albuquerque May 24, Republican presidential candidate Donald Trump criticized Gov. Susana Martinez (R-N.M.), saying, "Hey! Maybe I’ll run for governor of New Mexico. I’ll get this place going." (Reuters)

Republicans are testing out a theory. “What Trump is doing,” argues Peter Wehner of the Ethics and Public Policy Center, “is exactly what Rush Limbaugh and others have been begging Republican presidential candidates to do — to run a brutal, scorched-earth, anything-goes campaign. They now have their man.” So, is the nation longing for more invective, more viciousness, more accusations of scandal and conspiracy? A strong plurality of voters in Republican primaries seemed to agree. We will now see how the national electorate responds. As a starting move, Trump has accused Bill Clinton of rape and intimated that the Clintons are guilty of murder. It is hard to imagine going lower from here, but Trump will surely manage.

Some Republicans keep expecting Trump to finally remove the mask of misogyny, prejudice and cruelty and act in a more presidential manner. But it is not a mask. It is his true face. Good Republican leaders making the decision to support Trump will end up either humiliated by the association, or betrayed and attacked for criticizing the great leader. Trump leaves no other options.

Here is the problem in sum: Republicans have not been given the option of choosing the lesser of two evils. The GOP has selected someone who is unfit to be president, lacking the temperament, stability, judgment and compassion to occupy the office. This is a terrible error, which has probably cost conservatives a majority on the Supreme Court. But the mistake was made by Republican primary voters in choosing Trump — not by those who can’t, in good conscience, support him.

Read more from Michael Gerson’s archive, follow him on Twitter or subscribe to his updates on Facebook .