The biggest security threat facing our country at this moment isn't ISIS or Russia. It's the possibility that Donald Trump might be elected president of the United States.

That threat has been overshadowed by FBI Director James Comey's unprecedented interference in the election. So let's get back to what matters and stop digressing over unread emails.

The next president will be tested by our adversaries as soon as she or he takes office, at a time when the world is more unstable than at any time since the Cold War. We need a levelheaded experienced leader, not a trash-talking TV showman.

Former Defense Secretary Bob Gates nailed it when he said, "A thin-skinned, temperamental, shoot-from-the-hip, uninformed commander-in-chief is too great a risk for America."

And for the world.

When it comes to security, the dangers a Trump presidency present fall into three categories.

The first danger is the character of the man. The GOP candidate veers wildly when he deigns to talk about foreign policy, from an "America First" isolationism to a pledge to end the ISIS threat overnight. He shows little grasp of how the world works and little interest in listening or learning, insisting he is his own best foreign policy adviser.

Many Trump supporters believe he would have "brilliant" advisers who would compensate for his lack of experience. But seasoned Republican security experts have shunned Trump because - as 50 former GOP national security officials wrote in a public statement - he "lacks the character, values and experience to be president."

Trump's only experienced security adviser is retired Lt. Gen. Michael Flynn, who appears eager to promote "regime change" in Iran and other nations he thinks support our "enemies." For his part, Trump wants to junk the nuclear deal with Iran, which would leave the ayatollahs immediately free to seek a bomb.

It's unclear whether Trump would be ready to plunge America into new Mideast wars to overthrow leaders, but that seems where Flynn wants to lead him. Given Trump's hair-trigger temper and his careless talk about using nukes, it's unnerving to think about how he might overreact if a Mideast leader challenged him.

The second danger is Trump's reckless disregard for America's key alliances in Europe and north Asia. He suggests dismantling these ties at a time when Russia and China are in expansionist mode.

Most of America's NATO allies, especially in the Baltics and parts of Eastern Europe, are freaked out by Trump. So are the South Koreans and Japanese, given his suggestion that we might remove the U.S. nuclear umbrella that protects them; this would lead to a nuclear arms race in the Pacific with potentially horrific results.

Trump lies when he says the allies don't pay for U.S. security support - the Asians pay billions, and the NATO allies pay some, if not enough. What is worse, he treats these partnerships as if they are little more than a financial quid pro quo with U.S. troops as mercenaries for hire. He refuses to recognize the value of alliances of democracies at a time when threats against America are on the rise.

The GOP candidate seems unable to expand his worldview beyond the shoddy modus operandi of the Trump empire: extract every cent, then declare bankruptcy and go home.

The third danger is Trump's incomprehension of America's adversaries and how to handle them. Our adversaries don't see him as a tough leader. They see him as a "useful idiot" who can be played.

Susceptible to Vladimir Putin's flattery and eager for business deals in Moscow, Trump talks of partnering with Russia - and denies Moscow's electronic interference in U.S. elections. Putin will manipulate Trump's blindness in order to undermine NATO and support the rise of antidemocratic governments on the continent. Ditto for China, which will take advantage of Trump's strategic naiveté as it seeks to dominate the Pacific region and control Asian sea lanes.

As for ISIS, Trump seems not to have a clue how to fight the terrorists. He mainly focuses on attacking the patriotism of American Muslims; this will alienate the very communities whose cooperation is essential. And he keeps suggesting that America seize Iraq's oil fields. This is not only impossible (without another land war) and totally illegal, but also feeds ISIS propaganda that America's sole interest in the region is stealing the oil.

To sum up, at a time when the world is in turmoil, we have a candidate who alienates allies and helps adversaries. Far from reestablishing the United States as a global leader he will demolish America's remaining standing in the world. And I didn't even get to the economic damage Trump will wreak with his threats to start international trade wars

Trump supporters will argue that Hillary Clinton has already sunk America's global standing. If that were true, you wouldn't see America's democratic allies rooting for a Clinton victory, and expressing outright fear that Trump might win.

True, Clinton's term as secretary of state wasn't stellar. However, she is an experienced hand who will not do something reckless in a world verging on chaos. She supports a more forward-leaning U.S. role in the world (and was repeatedly thwarted by the Obama White House in her efforts). She would be no patsy to our enemies.

And Americans would not have to worry that a reckless narcissist had his finger on the nuclear trigger. For that reason alone Trump must not be elected president.