Russian President Vladimir Putin was an agent of the Soviet secret police | Natalia Kolesnikova/AFP via Getty Images Opinion Vladimir Putin, war criminal The Russian leader has a long record of inhumanity.

NEWARK, New Jersey — Russia’s criminal behavior in Syria is just the latest in a long string of crimes perpetrated by Russian President Vladimir Putin.

U.S. President-elect Donald Trump’s incoming administration may be unwilling to admit it, but Putin is a war criminal. The U.S. government may need to negotiate with him, but it should remember that he is a butcher.

Russia’s leader has a long record of inhumanity. He was an agent of the Soviet secret police, a criminal institution with a record that goes back to mass killings perpetrated by the henchmen of Soviet dictators Vladimir Lenin and Joseph Stalin. Putin knew the KGB’s record when he joined it in 1975, at the height of its crackdown on the Soviet dissident movement and just seven years after the country’s armed forces crushed the Prague Spring in Czechoslovakia.

When Putin came to power in 1999, he almost certainly approved, and perhaps even orchestrated, the bombings of two apartment buildings in Moscow, in which hundreds of innocent Russians lost their lives. As Amy Knight, a specialist on the KGB, argues, the evidence makes it “abundantly clear” that the Russian security service, the FSB (which succeeded the KGB), was “responsible for carrying out the attacks.” Concludes Knight: It is “inconceivable” that the bombings would have been done “without the sanction of Putin,” who exploited the panic they created to crack down on the Chechens and present himself as an indispensable leader.

During Putin’s years in office, a series of Russian democrats, journalists and opposition leaders have been killed in mysterious circumstances.

Putin used the bombings to reignite the Second Chechen War, in which he launched a massive air and land campaign that produced thousands of refugees, reduced much of the Chechen capital Grozny to rubble and killed at least 25,000 civilians.

Putin has funded, promoted, supplied and aided and abetted the Russian and pro-Russian terrorists in eastern Ukraine. Thus far, that war has taken 10,000 lives. It was Putin’s proxies who shot down Malaysia Airlines Flight 17 on July 17, 2014, killing 298 innocent people aboard.

Russia’s ruthless bombing of Syria’s civilian population and targets has been termed criminal by various Western leaders and human rights organizations, prompting U.S. Ambassador to the United Nations Samantha Power to ask her Russian counterpart: “Is there no act of barbarism against civilians, no execution of a child, that gets under your skin? That just creeps you out a little bit? Is there nothing you will not lie about or justify?”

During Putin’s years in office, a series of Russian democrats, journalists and opposition leaders have been killed in mysterious circumstances — the most prominent being Alexander Litvinenko, Anna Politkovskaya, Boris Nemtsov, Sergei Magnitsky, Natalia Estemirova, Sergei Yushenkov, Paul Klebnikov, Stanislav Markelov and Anastasia Baburova.

In October, Russian “nationalists” were allegedly involved in plotting to assassinate the prime minister of Montenegro, Milo Dukanović.

Some 12 opposition leaders from various parts of the former Soviet Union have also been killed in mysterious circumstances in Turkey, suggesting Russian assassins may be at work.

The record speaks for itself: Putin is a killer and war criminal — no different in the breadth and depth of his criminality than the Serbian war criminal, Slobodan Milošević. He must be treated as such by world leaders with even a minimal commitment to human rights and basic decency.

What should world leaders do?

First, they should openly condemn Putin’s behavior. Silence implies endorsement, and policymakers must understand their moral standing, and that of their countries, is on the line if they refuse to take a public stand.

One day, Putin will be gone, and Russia’s democratic opposition will be able to make their country a decent, law-abiding state.

Second, they should refuse to shake his hand, attend photo ops with him and create the impression that they accept his behavior. Unless Trump is willing to embrace former Ku Klux Klan leader David Duke in public, he should refrain from doing the same with Russia’s criminal leader.

Third, policymakers should avoid doing anything that aids and abets Putin’s criminal proclivities. Sanctions must not only be maintained, they should be intensified — not because they will change Putin’s barbaric behavior, but because the West and the world must demonstrate they oppose barbarism.

Most important, world leaders should actively defend Russian democrats and support Russia’s still-democratic neighbors, above all the Baltic states Georgia and Ukraine. One day, Putin will be gone, and Russia’s democratic opposition will be able to make their country a decent, law-abiding state. In the meantime, Putin must be told in no uncertain terms that the world will not tolerate any more imperialist land grabs and wars.

If the Trump administration fails to act accordingly, it will be announcing to the world that butchery is the new normal.

Alexander J. Motyl is a professor of political science at Rutgers University in Newark.