Plenty of presidents have invoked a higher power when making decisions.

But what if the president took things to the extreme, not just turning to providence when making tough choices but using the presidency — and all the power that comes with it — to further a radical religious agenda?

That situation isn’t dreamed up by some leftist lawyer but by Douglas MacKinnon, a former staffer to Sen. Bob Dole (R-Kan.). In his new novel, “The Apocalypse Directive,” MacKinnon whips up an exciting yet alarming tome that paints a morose future

of the war on terrorism.

Set in the near future, the novel centers on Ian Campbell, the deputy chief of staff to President Shelby Robertson, a religious zealot whose presidential decisions are based solely on his extreme view of Christianity. Campbell doesn’t share those beliefs; he’s a former Navy SEAL who’s jaded by the whole business of organized religion.

But to get the coveted White House gig, Campbell tricks Robertson into believing he shares the president’s religious views. Soon, Robertson is welcoming Campbell into a secret group calling themselves the “Christian Ambassadors,” whose goal is to advance the cause of Christianity and destroy those who oppose it.

Campbell soon learns that Robertson and his crew, made up of top military men and other government officials, are planning to launch a full-scale nuclear war to rid the earth of nonbelievers. Still fooling Robertson, Campbell is put in charge of a secret bunker built to provide a place for the Ambassadors to hide out during the slaughter, and he uses his new role to get more details on Robertson’s deadly plan before it is too late.

Campbell isn’t alone. Vice President Eileen Dale senses something amiss with the president, and partners with Campbell in a seemingly futile effort to put a stop to things.

Also in the picture is Rachel Hiatt, a New York Times reporter who reaches out to Campbell for any information he might have about her brother, Tom, who disappeared suddenly off the coast of Florida.

It’s clear MacKinnon’s novel is a warning to Americans to keep an eye on the spiritual activities of its leaders. The Ambassadors, for example, are based on the Christian Embassy, a real-life Christian ministry based in the Pentagon.

But the America in the book is far more violent than that of today. Aside from the conflicts in Afghanistan and Iraq, there are multiple terrorist attacks on the U.S. homeland, which killed more than 20,000 Americans. And by the end of the book, more attacks have taken place.

It can be a bit depressing, and so the book might not make for the best beach reading. But overall, “The Apocalypse Directive” is a good read; its fast pace and conspiracy plotline provide a thrill.

Readers familiar with the nation’s capital will enjoy how realistic MacKinnon is in describing the Washington, D.C., geography — in one scene, he manages to point out that there’s a Filene’s Basement located next to the Mayflower Hotel, for example.

But the book does tend to hit the reader over the head with its message against religious extremism. We get it — declaring war in the name of religion is a bad thing — we don’t need repeated soliloquies from the protagonist to grasp it.

Still, the reader is left wondering how much power the American people would yield to the president — and what that president could do with that power — should the battlefield in war on terror shift back to the U.S. homeland.

“The Apocalypse Directive” hits bookstores July 29.