Michael Morell was acting director and deputy director of the Central Intelligence Agency from 2010 to 2013. Mike Vickers was the undersecretary of defense for intelligence from 2011 to 2015. Both writers have served in Democratic and Republican administrations and endorsed Hillary Clinton for president.

Mr. Trump, with all due respect to you as the presidential nominee of the Republican Party, you cannot credibly serve as commander in chief if you embrace Russian President Vladimir Putin. The Russian leader has repeatedly shown himself to be an adversary of the United States. Putin, during his long tenure, has repeatedly pursued policies that undermine U.S. interests and those of our allies and partners. He has steadily but systematically moved Russia from a fledgling democratic state to an authoritarian one. He is the last foreign leader you should be praising.

Abroad, Putin has interfered in the internal affairs of a host of nations on his periphery — through information operations, manipulation of elections and direct support, including providing weapons, to insurgent groups. Most significant, in the past decade, Putin has invaded two neighbors, Georgia and Ukraine — including annexing Crimea, the first major land grab in Europe since World War II. Putin’s goal in doing this is to keep the nations of the former Soviet Union from linking their futures to that of Europe and the West. Do you back these actions?

Putin’s support of insurgents in eastern Ukraine resulted in the downing of Malaysia Airlines Flight 17, which killed 298 innocent civilians. Under Putin’s direction, Russian special forces provided the insurgents with and trained them how to use the air-defense system that brought down the plane. As intelligence officers who oversaw covert action, we can tell you that when a country provides overt or covert support to proxies, that nation is responsible for what those proxies do with that support. That makes Putin responsible for downing the airliner. Do you hold him responsible?

Also abroad, Putin has aggressively supported Syrian President Bashar al-Assad’s brutality against his own people. Putin’s significant intervention in Syria 12 months ago — via the Russian air force and Russian special forces — propped up Assad at the exact moment that the Syrian leader appeared to be losing his grip on power and might therefore be amenable to negotiating a transition of power. As such, Putin is in part responsible for the continuing civil war that has resulted in the deaths of 500,000 Syrians and displaced 10 million others, the greatest humanitarian crisis since World War II. Do you support what Putin has done in Syria?

On Sept. 7, during a town hall event hosted by MSNBC, Republican presidential candidate Donald Trump stated he would have “a good relationship” with Russian president Vladimir Putin. It wasn’t the first time he's been friendly towards him. (Adriana Usero/The Washington Post)

At home, Putin has jailed and killed political opponents. He has jailed and killed journalists. He has neutered the Russian media to the point that he is in complete control of the message reaching the Russian people. He has the popularity that you so admire only because he determines what the Russian people hear about him and his government. Do you support Putin’s violation of Russian law and his tramping of the civil rights of his populace, explicitly protected in the Russian constitution?

One of the more interesting questions is: Who is the biggest loser from Putin’s policies? Take Putin’s actions in Ukraine. One set of losers, of course, was the Ukrainian people, who had their aspirations crushed. Another was the West, particularly the United States, which looked impotent to stop the Russian aggression. But the biggest loser was the Russian people — because Putin has ended any hope of integrating the Russian economy with that of the West, Russia’s only hope for the future. Given this, do you still think Putin is a great leader?

At the Commander-in-Chief Forum on Sept. 7, you said that as long as Putin says nice things about you, you will say nice things about him. That is not a standard by which a president should make policy decisions. That should not even enter your calculus. Your only question should be “What is in the best interests of the United States?”

So, here is our challenge: Demand that Putin stop his aggressive behavior overseas. Demand that he stop his dictatorial moves at home. Tell him that you will live up to our NATO commitments and defend the Baltics if need be. Tell him that you want to work with him on solving the problems in the world — but that he must behave in order to do so. That is what a true commander in chief would do.