Treasury Secretary Steven Mnuchin took the highly unusual step during the past weekend of publicly explaining why he won’t resign.

He responded to Yale classmates who had written an impassioned open letter urging him to quit in protest over what they called (ridiculously overstating their case) President Donald Trump’s “support of Nazism and white supremacy.” There was no reason for Mnuchin — a busy man and one of the most important economic officials on the planet — to bother replying unless he feels a little defensive.

After Charlottesville, the question of the propriety of serving in the Trump administration gained new salience. Rumors swirled that economic adviser Gary Cohn was on the verge of quitting in disgust, and liberal journalists called for all good men and women to jump ship (“Every Trump Official With a Conscience Must Resign,” huffed The New Republic). This is wrongheaded. It’s much better for the country that as many responsible, talented people serve the Trump administration as possible.

Even if it isn’t easy. Working for Trump means being willing to put up with the possibility of humiliation of the sort that loyalist Attorney General Jeff Sessions suffered at the president’s hands. It means dancing around his outrageous statements and pretending to work for a more normal president. And it means courting social disapproval.

CEOs increasingly don’t want anything to do with Trump. Hollywood and representatives of the arts loathe him. And sports figures are leery. Trump is as personally radioactive as any president since Richard Nixon during his final descent.

This can’t be what a high-flying financier and movie producer like Mnuchin signed up for. But any Trump official who doesn’t think he is being forced to violate his personal conscience should stick it out.

The presidency is an important institution, and whatever fantasies his enemies may have of a rapid ending to his tenure, Trump is president. He needs good advice and competent help. There are obviously limits to how much he can be controlled, but he is susceptible to advice. It’s no accident that Trump hasn’t withdrawn from NAFTA, pursued a trade war with China or kneecapped NATO.

No one is irreplaceable, but it’s not as though Trump’s team is likelier to get stronger. Able people have been turning down job offers, warned off by the president’s volatility. The pool of talent available to Trump was never as large as that of a conventional president, and it has shrunk.

Surely, many of those around Trump enjoy the thrill of notoriety and proximity to power, as is true in any White House, but a sense of duty weighs as well. “There are people inside the administration,” Anthony Scaramucci said during his turn as White House communications director, “that think it is their job to save America from this president.” This puts it starkly and derisively, but no doubt accurately — especially when it comes to the generals.

The portfolios of Secretary of Defense James Mattis and national security adviser H.R. McMaster include the most consequential matters of state, and John Kelly is now running the White House as chief of staff. The administration’s credibility depends in large part on the service of these men.

If any of the generals, particularly John Kelly, were to quit and lambaste Trump on the way out the door, it might have a debilitating effect on his presidency. That sounds alluring to Trump’s critics. But crippled presidencies aren’t good for the country, and Trump was duly elected. So the generals are right to stay and serve their country in this capacity. Someone has to do it.

Rich Lowry is a syndicated columnist. He can be reached via e-mail at: comments.lowry@nationalreview.com.