Republican Presidential candidate Donald Trump addresses the Republican National Convention on July 21, 2016. (Toni L. Sandys/The Washington Post)
Opinion writer

If the startling lapses in judgment and deficiencies of temperament on display by Donald Trump over the past few days haven’t sufficiently freaked you out, then the prospect of the Republican presidential nominee becoming president of the United States with control of the nuclear codes most certainly will. And if it doesn’t, I hope you’ll be reasonably panicked after reading this.

Trump’s fingers on the nuclear button is such a frightening prospect that it is coming up with greater frequency. “Because when you have the nuclear codes at your fingertips and the military in your command, you can’t make snap decisions,” said first lady Michelle Obama last Monday. Democratic presidential nominee Hillary Clinton said last Thursday, “A man you can bait with a tweet is not a man we can trust with nuclear weapons.” Even Trump’s “Art of the Deal” ghostwriter Tony Schwartz told Jane Mayer of the New Yorker magazine, “I genuinely believe that if Trump wins and gets the nuclear codes there is an excellent possibility it will lead to the end of civilization.”

That might sound a bit hyperbolic or even laughable. But I’m taking Schwartz’s assertion seriously after talking to Malcolm Nance, a counterterrorism and intelligence consultant who runs the Terror Asymmetrics Project and is author of the New York Times bestseller “Defeating ISIS: Who they are, how they fight, what they believe.”

“The president has almost 100 percent control over the launch of nuclear weapons in any circumstance and under any condition he so chooses,” Nance told me in Philadelphia last week. “He needs to consult no one and can, if mad with power, personal vendetta or feeling national rage, launch an attack that the Constitution and his staffers cannot control.”

[The disgraceful bromance between Donald Trump and Vladimir Putin]

Anyone who has seen Nance on MSNBC knows that he doesn’t put up with loose talk about the use of nuclear weapons. He fears that Trump’s “not taking any cards off the table” when asked about dropping such a device on the Islamic State in Iraq and Syria is part of a troubling normalizing of a conversation that should be taken seriously, if it is to be engaged in at all. Not to mention Trump’s casual talk about letting Japan, South Korea and Saudi Arabia have such weapons of mass destruction.

“Mainstreaming of the nuclear risk by Donald Trump is the single most deadly thing we may do in our lifetimes,” Nance said. “It is akin to climbing the Freedom Tower in bowling shoes.”

Nance’s nuclear warning is backed up by Bruce Blair in a riveting piece in June for Politico magazine. The nuclear safety expert and research scholar at Princeton University argued that the presidency has become “a nuclear monarchy” where “the commander in chief has virtually unlimited power to rain down nuclear weapons on any adversarial regime and country at any time.”

In a frightening tick-tock, Blair outlines the actions that could lead to the annihilation of “hundreds of millions of lives … in a few agonizing hours.” And he impresses upon the reader that this sequence of horror can take between 12 minutes and 30 minutes (depending on where the missiles launch from) to get underway.

The order to unleash hell, Blair writes, “must be obeyed as long as it is constitutional—i.e., the president as commander in chief believes he or she is acting to protect and defend the nation against an actual or imminent attack.” Such a broad definition would be exceptionally dangerous in the hands of a man so tender that he promises to “open up” libel laws so that he can sue media outlets over stories he deems unfair.

Trump is so thin-skinned and quick to retaliate that he attacked the Gold Star parents of Humayun Khan, a Muslim American soldier who died in Iraq in 2004. The powerful address by Khan’s father before the Democratic National Convention last week was as much a rebuke of Trump’s xenophobic and unconstitutional proposal to ban Muslims from entering the United States as it was a stirring reaffirmation of this nation’s founding ideals.

Now imagine Trump entrusted with the awesome power and responsibility that comes with the nuclear codes. Nance told me there would be two ways to keep Trump from weaponizing petty slights and offenses. “If the president were to suddenly attempt to use the launch package for no reason the only way to stop him would be to convince him or, as the National Nuclear Command post staff told me … tackle him,” said Nance. He told me he has seen “a full-scale atomic simulation on the United States at a Presidential underground mountain bunker and it is terrifying that in 30 minutes this nation could be destroyed.”

“Someone would have to wrest control of the rest of the arsenal away from him,” Nance contributed, “by coup or mutiny in the armed forces.” Once upon a time, this was the stuff of fantasy. Or the fertile imagination of Tom Clancy or the producers of “Homeland.” But in the age of Trump, the unthinkable is terrifyingly close at hand.

Follow Jonathan on Twitter: @Capehartj