Adding a fourth nuclear power to NATO would go a long way toward restoring deterrence.

Bent on reestablishing Russia’s empire, dictator Vladimir Putin invaded Ukraine. His ambitions don’t stop at its western border. Could NATO, particularly the U.S., U.K., and France, be counted on to defend Poland and other front-line countries if Putin invaded?

Eastern Europe has reason to worry.

Due to feckless sins of commission and omission by the U.S. and U.K. during World War II, Stalin was able to enslave Eastern Europe. Franklin D. Roosevelt and Churchill never conditioned Soviet aid. They never sought to finish the war with Anglo-American armies as far east as possible. German entreaties to surrender on the western front were rejected. And anti-communist, anti-Hitler partisans were undercut.

When the Berlin Wall fell in 1989 and Soviet Union broke up in 1991, there was a brief, heady moment when freedom was on the march worldwide. Political scientist Francis Fukuyama famously declared “the end of history.”

The coals of despotism in Russia, however, were never extinguished. Heir to Ivan the Terrible and Stalin, ex-KGB man Putin took the reins from independent Russia’s first president, Boris Yeltsin, in 2000, and never to let go.

In the giddy post–Cold War environment, Western and some Eastern European leaders, assuming a world at odds with history, acted rashly.

In 1994, in thrall to the dogma that weapons, not men, cause wars, President Bill Clinton and U.K. Prime Minister John Major persuaded independent Ukraine to give up its nuclear arsenal, in exchange for a worthless parchment — the Budapest Memorandum. Russian President Yeltsin, Ukrainian President Leonid Krakchuk, Clinton, and Major pledged Ukraine’s territory wouldn’t be violated. Foolishly, Kyiv agreed.

In the same spirit, in 2006 Sens. Barack Obama and Dick Lugar sponsored legislation signed by President Bush to fund the destruction of vast stores of Ukrainian conventional arms and ordnance. Foolishly, Kyiv agreed.

If Ukraine had kept nuclear weapons, Putin’s tanks would not today be threatening Kyiv, and NATO’s eastern flank would be more secure.

In 2008, Russia invaded Georgia, seizing South Ossetia and Abkhazia. It should have been a wakeup call for a somnolent West.

Instead, in 2009, on the 70th anniversary of the Soviet invasion of Poland, President Obama shelved an anti-missile defense system in Poland and the Czech Republic to make nice with Putin. Obama, Secretary of State Hillary Clinton, and Russian Ambassador Mike McFaul pushed a fanciful “reset” with Putinist Russia. Their imagined kinder, gentler Putinist Russia was playing make-believe, and it was dangerous.

In 2014, Russia invaded Ukraine, flagrantly violating its Budapest Memorandum pledge. It shrugged off the West’s economic sanctions.

Former army intelligence officer Ralph Peters observes that economic sanctions are rarely successful, but they “allow us the comforting delusion that we have shown resolve while still behaving responsibly.”

While the Budapest Memorandum wasn’t a treaty, it’s hard not to characterize the U.S.’s and U.K.’s anemic response to Russia’s first invasion of Ukraine as a betrayal.

Led by Senate Foreign Relations Committee Chairman Bob Menendez, Congress approved arms for Ukraine. Not wanting to provoke Putin, Obama refused to provide them.

And this year, Putin took the measure of the putative leader of the free world, feeble President Joe Biden, and decided the time was ripe to swallow Ukraine whole.

The 21st-century tsar’s nuclear saber-rattling spooked Biden, causing him to veto giving Polish MiGs to Ukraine. Nobody wants a nuclear war with Russia, but the weaker the West, the more likely greater war.

If Putin conquers Ukraine, he will look to devour Georgia and Moldova, and to test NATO, by invading the Baltics, Poland, or Romania.

Peters warns that “there is no deterrence without risk, but there is nothing but risk in the absence of deterrence.”

NATO deterrence is in America’s interest — the threat of retributive violence against Russia is credible.

Three NATO members have nuclear weapons, but Russia isn’t going to attack the U.S., U.K., or France. Washington could supply Poland with a small nuclear arsenal, in a stroke making deterrence convincing.

Adding a fourth NATO nuclear power on its eastern front would reduce the likelihood of Putin’s tanks rolling on Warsaw, Vilnius, Tallinn, or Riga.