New Haven — This week the American business community did something virtually unprecedented in its history: It shunned the call to national service by the commander in chief. In the wake of President Trump’s horrifying, un-American equivalence of neo-Nazi storm troopers with the peaceful counter-demonstrators at their weekend rally in Charlottesville, Va., first one, then another, then a flood of chief executives quit his business councils. Now they need to do more.

The courageous Ken Frazier, Merck’s revered, high-performing C.E.O., was the first to speak out. In his resignation letter on Monday, he wrote, “As C.E.O. of Merck and as a matter of personal conscience, I feel a responsibility to take a stand against intolerance and extremism.” Mr. Frazier is something of a modern-day Joseph N. Welch, the Boston lawyer who in 1954 punctured the demagogy of Joe McCarthy by asking the senator in a hearing, “Have you left no sense of decency?”

Mr. Frazier is the epitome of the American dream, having grown up in gang-infested North Philadelphia, the son of a well-read custodian, to become one of three black Fortune 500 chief executives at the time. President Trump predictably attacked him, which immediately backfired; over the next several days, C.E.O.s who had once shunned politics came to his vocal defense, including the heads of Walmart, Intel, BlackRock and IBM.

Chief executives, we’ve been told, long refused to criticize the president because of overlap between his supporters and their customers, and because of the president’s vicious Twitter game. But the real problem was that no one wanted to go first; once Mr. Frazier stepped forward, he gave cover to the rest.