WASHINGTON — Beto O'Rourke, innovative for interpreting a failed Senate campaign as a steppingstone to the presidency, is now famous for (1) his use of profanity on the campaign trail, (2) his pledge that "hell, yes" he wants to confiscate AR-15s and (3) his proposal to tax religious institutions that don't approve of gay marriage.

This is not the normal substance of presidential ambitions. Few young people nursing political dreams say: "When I grow up, I want to be a foul-mouthed, overreaching, anti-religious culmination of every exaggerated liberal stereotype and the embodiment of every fevered conservative nightmare." Perhaps O'Rourke was just precocious in that way. It is more likely, however, that he was led in this direction by the increasingly desperate pursuit of a spotlight that fell on him once, and briefly.

Some responsible Democrat needs to sit O'Rourke down and tell him it is not worth winning the Democratic nomination in ways that guarantee a reelection landslide for Donald Trump. And that it is not worth losing the Democratic nomination in ways that badly hurt the eventual Democratic nominee.

The loyalty and enthusiasm of Trump's base of support in the GOP — especially among white evangelicals — are ensured by apocalyptic fears. The election of a Democratic president, the story goes, would end America as we know it, and usher in an era of anti-Christian persecution. By this logic, conservative Christians view Trump as a thug who fights in their favor.

It is a unique conception of religious social engagement: Hire someone to do unto others what you fear they will do to you. This is Christian politics as protection racket. It is theologically inadequate — and damaging to the public standing and witness of evangelicals. But it makes more sense as a political strategy when the threat from secular liberalism becomes less imaginary.

Asked in a CNN town hall if churches and religious organizations should lose their tax-exempt status if they oppose same-sex marriage, O'Rourke responded: "Yes. There can be no reward, no benefit, no tax break for anyone, or any institution, any organization in America that denies the full human rights and the full civil rights of every single one of us. And so, as president, we're going to make that a priority and we are going to stop those who are infringing upon the human rights of our fellow Americans."

Where to begin? Was O'Rourke really promising to withdraw tax benefits from people — "anyone" — who do not approve of same-sex marriage and not just institutions? Would someone who is internally divided get a partial tax break? What if they changed their mind during the third quarter of the fiscal year?

Presumably this was O'Rourke getting carried away in his disdain for religiously conservative Christians and Muslims. But the problem gets no easier in applying the O'Rourke rule to institutions and organizations. How does one decide if, say, one United Methodist Church is in violation of the new IRS rule and another is not? By the minister's view on same-sex marriage? By counting the majority position of the congregation? By the view of the local bishop? By the view of the national church? Or the international communion?

The taxation of churches according to their moral views would be inherently and massively intrusive. In the majority opinion of Walz v. Tax Commission of the City of New York, Chief Justice Warren Burger argued that any taxation of churches would mandate extensive interaction between government and religion. "The exemption creates only a minimal and remote involvement between church and state, and far less than taxation of churches," he said. "It restricts the fiscal relationship between church and state, and tends to complement and reinforce the desired separation insulating each from the other."

The proposed O'Rourke rule would only really work by getting rid of the tax "reward" for all religious institutions — institutions which some progressives seem to view with thinly concealed contempt. But the exemption is not really a reward. Through it, according to Burger, the tax code "simply abstains from demanding that the church support the state." And, as a practical matter, changing this treatment would cripple the provision of social services to the poor and suffering, since religious institutions feed the hungry, treat substance abuse, resettle refugees, provide health care, housing, legal services, mentoring, literacy education, employment training and make countless other humane contributions to the common good.

O'Rourke's proposal is manifestly foolish — an example of ideology unleashed by ignorance. The eventual nominee of the party — who will not be O'Rourke — will either repudiate this idea or grant Trump a stout stick to beat Democrats with.

Michael Gerson's email address is michaelgerson@washpost.com.