Wayne Grudem, the theologian and ethicist whose writings have provided the intellectual grounding for a generation of highly conservative evangelicals, came out last week with a startling endorsement of Donald Trump. Startling, because while Trump has garned the backed of some senior evangelical leaders – certainly more than Hillary Clinton – they have not been falling over themselves with enthusiasm for him. One the contrary, one of their most respected figures, Russell Moore, has been resolute in maintaining his utter scorn for Trump's candidacy.

What's galvanised comment about Grudem's position, however, is his statement that voting for Trump is "a morally good choice" for evangelicals. And he says this in spite of also listing his flaws: he is egotistical, bombastic, and brash, often lacks nuance in his statements, is insulting, vindictive and unfaithful and wants to bomb the families of terrorists. "These are certainly flaws, but I don't think they are disqualifying flaws in this election," says Grudem.

And for the avoidance of doubt, it isn't just because he's not Clinton: "In fact, it is the morally right thing to do."

The US evangelical perception of Hillary Clinton as untrustworthy to the point of being demonic is rather strange, given her relatively high rating by the Politifact checker (most of what Trump says is false, on the other hand). On the other hand, for pro-lifers, her position on abortion is more genuinely problematic. She is unwaveringly pro-choice, and has argued against restrictions on late-term abortions. Furthermore, she's opposed to the longstanding Hyde Amendment, that prevents Medicaid healthcare covering abortions. A widely-shared social media post claiming she and Bernie Sanders wanted to extend abortion rights to 36 weeks has been shown to be false, but she is still a long way to the left of most evangelicals on a key issue.  

But it's Grudem's reasoning about Trump that's interesting – and particularly the way he turns a political contest into a moral one. In doing this he is arguably contributing, to a significant degree, to a process of evangelical degradation that has got many observers seriously worried.

The problem is not that Grudem is a Republican. Almost half of Americans are, just as almost half are Democrats. The problem is the way he takes complex and nuanced situations and turns them into simplistic, good-or-evil positions in which one is clearly Godly and the other clearly isn't. Grudem uses religious language to back up positions that don't derive from religion at at all. And in doing so he prostitutes theology in the service of a party.

His methodology is to describe Clinton's position as "liberal" and Trump's as "conservative". "This year we have an unusual opportunity to defeat Hillary Clinton and the pro-abortion, pro-gender-confusion, anti-religious liberty, tax-and-spend, big government liberalism that she champions," he says. "I believe that defeating that kind of liberalism would be a morally right action."

Grudem then spends around 5,000 words comparing "the results we could expect from a Clinton presidency with what we could expect from a Trump presidency". Much of it is based on his predictions about what would happen if either liberal or conservative justices were appointed to the Supreme Court. It's fair to say his forecasts for a Clinton-appointed court are fairly apocalyptic, whereas pretty much everything in the garden is rosy for a Trump-appointed one.

However, it's also fair to say he makes some very large assumptions, both about their respective picks and the lines the court would take in consequence. It's not unreasonable to point out that Grudem, while he may know quite a bit about theology, is no expert on the law. And when he writes: "The nation would no longer be ruled by the people and their elected representatives, but by unelected, unaccountable, activist judges who would dictate from the bench about whatever they were pleased to decree. And there would be nothing in our system of government that anyone could do to stop them," he is not writing fact but opinion – and opinion based on very shallow foundations.

Liberal judicial takeover

He's raising the spectre of a judicial takeover by "liberals" who are fundamentally anti-Christian and opposed to what right-thinking people believe. Abortion, religious liberty, freedom of speech, same-sex marriage and transgender rights – Grudem's vision of a Clinton presidency is of a totalitarian state where dissent is crushed and Christians face persecution for daring to hold traditional Christian beliefs. There's no acknowledgment that in a modern democracy – in which people believe all sorts of different things and Christians don't get to make the rules – rights compete and everyone has to give a little. There's no understanding that in order to make society work, to give everyone a stake and voice, there needs to be negotiation and compromise. There's just a terrible simplification: either you are with God, or you are with Hillary Clinton. He's too canny to say it straight out, but that's the implication of everything in his piece.

However, it's after he finishes with his Supreme Court predictions that his argument really tears loose from its moorings in morality. From the big picture he descends to specifics.

Trumps wins over Clinton because he'd lower taxes more than her. He's promised to solve the problems of poverty among minority groups, whereas she'd "strangle businesses with high taxes". Trump would expand the military, while Clinton would cut it – no evidence cited. Trump would "finally secure our borders" (presumably the wall with Mexico) while Clinton will "continue to allow in what she thinks will be thousands of future Democratic voters".

Trump will destroy ISIS, Clinton will not – no mention of Trump's repeated failure to say how he would do so. Trump is pro Israel, Clinton is not. Trump is pro oil, Clinton is green. Trump will end the "compulsory moral degradation forced on us by a liberal agenda" including letting transgender people use their bathroom of choice; Clinton will "perpetuate and expand" these policies.

And on healthcare, Trump will repeal Obamacare, which is "ruining the nation's health care system", while Clinton will "continue to work relentlessly toward federal government control of our entire health care industry". (According to Forbes, by last year Obamacare had resulted in the number of uninsured Americans falling below 10 per cent for the first time ever; it has helped an estimated 16 million previously uninsured citizens get cover.) Finally, Trump will protect the "unprotected" – lower-income people who face insecurity and poverty.