If you wonder why young people are leaving organized religion in droves, look no further than last week’s National Prayer Breakfast.

Many who care about religion and its fate have condemned President Trump’s vindictive, self-involved, God-as-an-afterthought speech at the annual gathering. By contrast, his backers were happy to say “Amen” as they prepared to exploit religion in one more election.

My Post colleague Michael Gerson, a beacon of moral clarity in the conservative evangelical world, noted that Trump’s address was a tribute to his “remarkable ability to corrupt, distort and discredit every institution he touches.”

Gerson is right, but I confess that there has always been something troubling about the prayer breakfast. I don’t doubt the sincerity of the faith of many of its organizers. There have been moments when politicians, including presidents, have used the occasion to promote humility in the face of God’s judgment and call each other to fellowship across their political differences.

Nonetheless, the whole exercise seems idolatrous. The gatherings encourage the suspicion that many politicians are there not because of God but because of their own political imperatives. They want to tell the world how religious they are and check the faith box on the advice of their political advisers. You worry that this is as much about preening as praying.

And, as historian Kevin Kruse pointed out in his book “One Nation Under God,” the prayer breakfast was a component of a public elevation of religion in the 1950s designed at least in part to serve the cause of conservative politics.

In his always crude but always revealing way, Trump has exposed the underside of long-standing political habits and practices. He is not the first politician to exploit religion. He just does it in a way so at odds with the core tenets of the Christian faith he claims to uphold that he pushes the hypocritical aspects of public religion to a breaking point.

Trump’s religious supporters, most of whom preach the most conservative versions of Christianity, either don’t realize or don’t care that they are ratifying what so many young people have come to believe about religion: that it is nothing but a cover for conservative politics, that it is far more about identity than faith, that it upholds a static traditionalism rather than a living tradition.

Thus do 4 in 10 Americans under 40 declare that they have no religious affiliation whatsoever. They are far from devoid of profound moral commitments, and some of them still think of themselves as spiritual. But organized religion just doesn’t speak to them anymore.

It does not make me happy to write these things because I have always believed that faith has a lot to teach us about public life. For the believer, separating faith from politics is neither desirable nor possible.

My own political views have been deeply influenced by such religious thinkers as theologian Reinhold Niebuhr, Martin Luther King Jr. and, more recently, Pope Francis. There can be no denying that many acts of justice and mercy have been prompted by moral demands more elevated and important than the imperatives of this world.

This is why Utah Republican Sen. Mitt Romney’s reasoning for voting to convict Trump was so blessedly subversive. He invoked God not to sacralize a regime but to challenge his conscience. Thus did he offer an indirect but unmistakable rebuke to Christians who say Trump deserves their fealty because he is protecting their interests and defending their culture.

It’s a useful rule that when our religious faith tells us to do the thing that would be easy and convenient, we are almost certainly mistaking the voice of our own self-interest for the voice of God. I don’t pretend to have any certainty about when our thoughts really are divinely inspired, but I suspect this is more likely to be true when a quiet religious voice asks us to do the hard thing — the thing we wish we didn’t have to do.

Of course, I agreed with Romney. I admired the courage both he and Sen. Doug Jones (D-Ala.) demonstrated in casting politically and personally difficult votes to convict the president.

I acknowledge you have every right to be suspicious that I’m as inclined as anyone to see faith as blessing my own politics. Nonetheless, Romney showed us how religion is most usefully invoked in public life: when it prompts self-doubt rather than self-celebration, when it encourages us to build solidarity with those unlike us and when it promotes dissent rather than conformity.

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