Donald Trump thinks his "greatest contribution to Christianity" would be the repeal of the Johnson Amendment, that prevents churches and pastors overtly campaigning for political parties. It's easy to see why he wants it: Trump has racked up quite a few not-quite-endorsements from evangelical conservatives who'd love to use their pulpits as campaign platforms for him.

At yesterday's Republican National Convention meeting, marked by rowdiness, desperation and farce as Melania Trump was accused of plagiarising Michelle Obama, one moment stood out as exemplifying the exact reason American lawmakers would be crazy to let Trump make that contribution.

Rev Mark Burns, an African-American pastor, was asked to pray. He reminded the audience that "our enemy is not other Republicans, but is Hillary Clinton and the Democratic Party" And he continued by thanking God for Trump, saying: "We're thankful that you are guiding him, that you are giving him the words to unite this party, this country, that we together can defeat the liberal Democratic Party... Because we are the United States of America, and we are the conservative party under God."

Furthermore: "To defeat every attack that comes against us, protect the life of Donald Trump. Give him the words, give him the peace, give him the power and authority to be the next president of the United States of America. In Jesus' name – if you believe it, shout 'Amen!'"

And they did.

In 1968 Billy Graham publicly supported Nixon's candidacy, but he prayed appropriate prayers at both the Republican and Democratic National Conventions.

What's so alarming about Burns' prayer – and what should absolutely terrify those already alarmed about the prospect of a Trump presidency – is the way he enlists God on the side of conservative Republicans.

In fairness, he's not the only one. Conservative evangelicals have routinely painted the Republican agenda as the Christian one and demonised Clinton in this most bitter of contests, bringing back memories of the 2004 Bush-Kerry election. Notoriously, in a message to Liberty University students in the seminary chapel, Jerry Falwell told students then to "vote for the Bush of your choice".

But when a candidate for the highest office in the land seeks to baptise his political crusade and make it a fundamentalist religious one, alarm bells should start ringing. Because with politics, you can disagree. You have to try first to win the argument, then to convince people you've won it. There's room for doubt, and you can concede your opponent has a point while at the same time vigorously defending your position. You can even be friends with her, if not best friends. It's just politics.

But add the language of "enemy" into the mix, try to conscript God on to your side, and make the whole contest not about right and wrong but about good and evil, and you've opened the door to something dark and dangerous. Because the thing about this particular brand of religion is that it's absolute. There's no room for negotiation or reconsideration. At the RNC yesterday Mark Burns tried to weaponise prayer and cast all Trump's opponents as God's enemies.

This ties in with far too much rhetoric from the Republican camp, about Muslims, Democrats and Clinton in particular. And it's rhetoric that should be categorically rejected, not just because of the unpleasant tang of burning heretics it brings with it on the breeze, but because it is fundamentally unbiblical.

Joshua 5:13-15 tells of an encounter between Joshua and (presumably) an angel before the Battle of Jericho. Joshua asks, "Are you for us, or for our enemies?" "Neither," the man replies, "but as commander of the army of the Lord I have now come." In other words, God is on no one's side; it's for us to be on his.

In his prayer, Burns crystallises what's wrong with Christian support for Trump. His campaign has become an ersatz evangelistic campaign, drawing on the same emotions and the same division of the world into the saved and the lost. The devil is Clinton; Trump is the saviour.

And Jesus looks on and weeps.

Follow Mark Woods on Twitter: @RevMarkWoods