When it comes to assessing the presidential race, I prefer to listen to the spies. They tend to be brutally unsentimental, see through the nonsense and cut to the cold, hard bottom line. And right now, two of the world's foremost former spymasters are sending uncoded messages about what it will mean for America and the Western alliance if Mr Donald Trump is elected president.

Ladies and gentlemen, I introduce former Central Intelligence Agency (CIA) director Robert Gates and his long-time nemesis and former KGB agent, President Vladimir Putin of Russia. Mr Putin is voting Trump. Mr Gates is not.

In an essay in The Wall Street Journal, Mr Gates, who also was defence secretary for presidents George W. Bush and Barack Obama, criticised both Mrs Hillary Clinton and Mr Trump for failing to take the threat posed by Mr Putin's Russia seriously. But Mr Trump, Mr Gates added, has gone places with Mr Putin no would-be American president should: "Mr Trump's expressions of admiration for the man and his authoritarian regime are naive and irresponsible."

Yes, Mrs Clinton has her own credibility issues on national security, Mr Gates explained, but "Donald Trump is in a league of his own. He has expressed support for building a wall between the US and Mexico; for torturing suspected terrorists and killing their families; for Mr Putin's dictatorial leadership and for Saddam Hussein's non-existent successes against terrorism. He also has said he is for using defence spending by Nato allies as the litmus test on whether the US will keep its treaty commitments to them; for withdrawing US troops from Europe, South Korea and Japan and for the latter two developing nuclear weapons - a highly destabilising prospect".

Mrs Clinton still has time to address her judgment and credibility issues and earn votes of people like himself, Mr Gates said. As for Mr Trump, he said, "on national security, I believe (he) is beyond repair. He is stubbornly uninformed about the world and how to lead our country and government, and temperamentally unsuited to lead our men and women in uniform. He is unqualified and unfit to be commander-in-chief".

I admire Mr Gates for speaking out. Not enough attention has been paid to the national security implications of a Trump presidency.

I'm certain you'd see US military officers and government officials quitting if Mr Trump ordered them to torture captured terrorists, go house to house to evict illegal immigrants, start trade wars with China and Mexico or ban Muslims. Mr Trump the chaos primary candidate became the chaos presidential nominee, and you can bet he'd be a chaos president.

Being unpredictable as a leader is fine, if you know where you're going and it is a tool to get you there by keeping foes off balance. But being unpredictable because you have no discipline; because you think issues like the Islamic State in Iraq and Syria (ISIS) are just a manhood test; because you have not studied the issues so anything can come out of your mouth; and because you don't realise that when we tell countries like Japan or South Korea or our Nato allies that we might not protect them from Russia or China, they will go get their own nukes and make the world even less stable - well, that kind of unpredictability is how alliances get broken, messes get made and wars get started.

That's why Mr Putin is licking his chops. It is no accident that he praised Mr Trump as "a really brilliant and talented person, without any doubt". It is also no accident that his cyber agents have hacked the Democratic National Committee and the Clinton campaign - to create embarrassing leaks - while ignoring both Mr Trump and the GOP. It's because Mr Putin knows the same thing that Mr Gates does: A President Trump would keep Washington and the Western alliance in turmoil.

Moreover, Mr Trump has told so many baldfaced lies in the last year, I can't imagine what would happen if he had to take America into a war. Who would trust that he was telling the truth about anything?

Also, because of how he has disparaged our Nato allies, it is impossible to envision him leading the alliance - particularly if we have to blunt further Russian expansion. And how exactly is he going to enlist Arab Gulf nations against ISIS or to counterbalance Iran, having stated that their Muslim citizens should be banned from entering the US?

Who will want to work with him? Mr Trump is constantly saying extreme things and then taking them back or claiming to be misunderstood. Consider the havoc that will wreak with our diplomacy.

That's why the cynical Mr Putin admires him. Mr Trump, narcissist that he is, thinks it's because Mr Putin really admires his leadership qualities. No, Donald. It's because Mr Putin knows a mess-maker when he sees one, and the thought of America being led by a man who would be wildly unpopular simultaneously in Europe, Beijing, Mexico, South America and the Muslim world is for Mr Putin a dream come true. The old KGB could never make that happen.

So, young people, listen up: Hillary doesn't light your fire? OK, I agree, she is a flawed candidate. But she can responsibly manage the affairs of state. Mr Trump is beyond repair and won't just light your fire - he'll burn the house down. Ask the old spies.

N YTIMES