Many people are getting their history and their definition of impeachment wrong by asserting that what forced Nixon to resign was the revelation in August 1974, very late in the process, of a recording of his trying to obstruct justice. This leads them to the erroneous conclusion that it’s essential to find a “smoking gun” to impeach a president.

In fact, even before that tape was released, the House Judiciary Committee had already approved three articles of impeachment against Nixon. It was widely understood that opinion had moved so strongly against him that the House would approve those articles and the Senate would vote to convict Nixon on those grounds. The tape simply hastened the finale.

By far the most important article of impeachment approved by the House committee on a bipartisan basis was Article II, which called for the punishment of Nixon for abusing presidential power by using the executive agencies (such as the Internal Revenue Service) to punish his enemies and for failing to uphold the oath of office to “take care that the laws be faithfully executed.” It also said, significantly, that a president could be held accountable for a pattern of abusive or even illegal behavior by his aides.

Madison and Hamilton didn’t say anything about holding off on impeachment because it would be politically risky. It’s hard to imagine they’d put political convenience on the same footing as the security of the Constitution. And the Democrats who prefer to substitute the 2020 election for an impeachment fight don’t appear to have considered the implications if Mr. Trump were to win: Would that not condone his constitutional abuses and encourage his authoritarian instincts?

Moreover, the report by Robert Mueller, the special counsel, left clear openings, perhaps even obligations, for Congress to act. Mr. Mueller did not say that there had been no collusion, or conspiracy , or whatever between Russian oligarchs and intelligence agents with ties to the Kremlin and members of the Trump campaign — in fact he traced the considerable traffic, or what he called “links” and “contacts,” between them in some detail. But he wrote that he couldn’t “establish” coordination between the Trump campaign and the “Russian government.” In his view, to win a court case, he had to prove some sort of specific agreement between the Trump campaign and that government.

While Mr. Mueller cited 10 likely instances of obstruction of justice on the president’s part, he said he stopped short of charging Mr. Trump with that crime largely because of a Justice Department rule that’s not law but is taken as Holy Writ. Mr. Mueller even invited Congress to address the matter. Almost as a plea, he added that “no person is above the law.”

The Democrats may succeed in avoiding a tumultuous, divisive fight over impeachment now. But if they choose to ignore clear abuses of the Constitution, they’ll also turn a blind eye to the precedent they’re setting and how feckless they’ll look in history.