For three years, we were lucky. We made it through most of President Trump’s term in office without facing a crisis that required great presidential leadership. Now, our luck has run out, and we are on our own.

It is difficult to overstate the scope of the challenge that covid-19 presents to the nation and the world — or the tragic inadequacy of Trump and his administration. Sometimes, an underestimated president improbably rises to meet the moment: Think of Harry S. Truman rebuilding a free and peaceful Europe after World War II, or George W. Bush rallying the nation with his bullhorn in the ruins of the World Trade Center. But Trump has become smaller, pettier, more self-absorbed. He failed.

There is much that the nation desperately needs right now: more financial help for the tens of millions of newly unemployed; more support for small businesses on the brink of failure; more consistent guidance on surviving the crisis day-to-day. But there is one need that surpasses all the rest, because meeting it could change everything and put us on the path to recovery: quick, reliable, universal testing that can tell us who has been infected with the novel coronavirus and who has not.

Trump could make that happen. Bizarrely, and tragically, he refuses to act.

Private companies, universities and government scientists have quickly developed an array of tests. Trump should use his powers under the Defense Production Act to mandate production of enough test kits — and the build-out of enough laboratory capacity to process all those tests promptly — to make it possible for every American to be tested periodically. That information would allow the nation to function at some reasonable level for the 12 to 18 months until, hopefully, we have an effective vaccine.

This would be a massive logistical effort, analogous to the way automobile companies shifted to war production during World War II. It would necessarily involve sourcing much-needed equipment from other countries, especially China. Only the federal government has the capacity to design and oversee such a program. Instead, Trump refuses to do his job.

“States can do their own testing,” he has said. “We’re the federal government. We’re not supposed to stand on street corners doing testing.”

That is precisely what the federal government should be doing. But it’s a daunting task, requiring consistent, determined leadership — which Trump will not even try to provide. What he gives us instead is “The Trump Show,” a daily televised farce in which he tries to keep alive his reelection hopes by deflecting responsibility and trying to change the subject.

Governors have had to fill the vacuum. Gov. Andrew M. Cuomo (D) of New York, whose state is the epicenter of infection in this country, has displayed steady leadership and continues to give must-see daily briefings that provide not just solid information but also a welcome measure of comfort. Govs. Jay Inslee of Washington and Gavin Newsom of California, both Democrats, reacted to covid-19 with early stay-at-home orders that kept infections, hospitalizations and deaths in their states relatively low.

Cuomo and Newsom have each organized regional consortia of states, one in the Northeast and one on the West Coast, that will coordinate the steps they take toward reopening once that process can be started. Governors of seven Midwest states reportedly are forming a similar compact. Cuomo said Thursday that the Northeast states will keep their social distancing orders in place at least through May 15. Such coordinated blocs of states will surely do all they can to bring testing capacity up to scale — but it is difficult to see how they could even get close to universal testing without help from the federal government.

Private companies will play a role as well. Amazon chief executive Jeff Bezos (who also owns The Post) said Thursday that he hopes to soon begin regular testing of all of Amazon’s 900,000-plus employees. Other big employers are likely to follow. But that will be just a start.

Thus far, only about 3.3 million Americans have been tested — out of a population of 328 million. Unbelievably, according to figures from the Centers for Disease Control and Prevention, fewer tests are being done this week than last week. How is this possible? Does American exceptionalism now mean hapless incompetence rather than resolute strength?

Meanwhile, Trump is reportedly still fixated on the dangerous fantasy of reopening the country in two weeks and filling professional sports stadiums with cheering fans. We will win this war because we must. But victory won’t come because of Trump; it will come in spite of him.

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