In the fall of 1991, Stanislau Shushkevich received me in his office in the cavernous Belarus Supreme Soviet. I asked the new leader of the one-month-old nation how many nuclear bombs were in Belarus. Shushkevich, a physicist by training, answered: “I have no idea. Ask the Russians. The Soviet Army controls all the nuclear weapons here.”

Fast forward three decades. President Putin plans to return nuclear weapons to Belarus this summer. As before, the Kremlin will control the nukes. The tale of the intervening 30 years can be seen by Iran, North Korea, and others as a lesson in the perils of unilateral nuclear disarmament. Just ask President Clinton.

The story started out well. From the collapse of the Soviet Union, four nuclear states emerged: Russia, Ukraine, Belarus, and Kazakhstan. In 1991, Ukraine was actually the world’s third-largest nuclear power, after Russia and America. Ukraine inherited 2,321 nuclear bombs. Kazakhstan had 1,410, about three times the current estimated arsenal for China. Belarus had 81, comparable to the current estimated arsenal of Israel.

In a masterstroke of international diplomacy, the three former Soviet republics agreed to sign the Nuclear Non-Proliferation Treaty. Under the terms of the deal, all three countries blew up missile silos, and then transferred some missiles and all nuclear weapons to Russia. In return, each of the three countries got a Budapest Memorandum.

Finalized at Budapest in December 1994, each document was signed by the relevant national leader and the leaders of the United States, Britain, and Russia. Among those attending was Donald M. Blinken, then America’s ambassador in Hungary. His son, Antony Blinken, is now Secretary of State.

Under the terms of the Budapest memoranda, America, Britain, and Russia guaranteed the sovereignty of each nation within its current borders. For Americans, the “loose nukes” nightmare was over. At Pervomaisk, one of the five Soviet Rocket Army missile centers in Ukraine was converted into a Cold War museum. Tourists peered down silos and took elevators to underground command posts.

In the spring of 2014, when President Obama was in office, Russia ignored Ukraine’s Budapest Memorandum and seized Ukraine’s Crimean peninsula and half of its Donbass region. In response, lawyers at the State Department said that the Budapest Memorandum was just that, a memorandum, not a treaty ratified by the American Senate.

While many Americans saw the Budapest Memorandum as a footnote to history, the message was not lost on the mullahs in Iran or the Kim family in North Korea. A country gave up its nuclear arsenal in return for guarantees on a piece of paper. Then one guarantor invaded the denuclearized nation.

Now, Shushkevich’s successor, the Belarus leader Alexander Lukashenko, is tearing up his Budapest Memorandum. Dependent on Mr. Putin for his survival, Mr. Lukashenko conducted a “referendum” last year that approved abandoning the nation’s non-nuclear status.

For many analysts, this is part of Mr. Putin’s plan to return to the Soviet era. Then, Belarus, Ukraine, and Kazakhstan had voting rights in the United Nations, but were totally subservient to Moscow.

“It will be hard for any subsequent government in Minsk to distance itself from Russia economically and politically,” Belarussian analyst Artyom Shraibman wrote last week for the Carnegie Endowment for International Peace. “But once Belarus starts hosting Russian nuclear weapons, it will be downright impossible.”

Mr. Putin’s announcement about stationing nuclear weapons in Belarus came two days after the Chinese party boss, Xi Jinping, completed a state visit to Moscow. In their joint communique, Messrs. Xi and Putin agreed that: “All nuclear-weapon states should refrain from deploying nuclear weapons abroad.”

 “Putin’s subsequent decision to place nukes in Belarus may well be an indication of his frustration over China’s obvious reluctance to back Russia more forcefully,” Peter Dickinson writes for the Atlantic Council in an essay titled: “Putin’s nuclear saber-rattling is a sign of dangerous Russian desperation.”

Russia is running out of arms. Photo experts say trainloads of Stalin-era T-54 tanks are being shipped west from a storage depot created in the Russian Far East during the Korean War. Ukrainian forensic experts say that some of the missiles rained down on Ukraine recently were the same missiles that Ukraine shipped back to Russia in the mid-1990s. Aimed at Ukrainian cities, these missiles carried conventional warheads.

With a major Ukrainian counter-offensive expected shortly, Belarus’ Mr. Lukashenko called last week for an immediate, unconditional ceasefire in Ukraine. “It is impossible to defeat a nuclear power,” Mr. Lukashenko warned in annual address to Belarussian lawmakers. “If the Russian leadership understands that the situation threatens to cause Russia’s disintegration, it will use the most terrible weapon.” He hailed “the return to Belarus of nuclear weapons withdrawn in the 1990s.”

In Ukraine, some now feel that one-sided nuclear disarmament was a mistake. Three small political parties advocate building nuclear weapons. Mr. Clinton, who signed the Budapest deals for America, is having second thoughts.

“I feel a personal stake because I got them [Ukraine] to agree to give up their nuclear weapons,” he said in a lengthy interview aired Wednesday on Irish TV RTÉ. “And none of them believe that Russia would have pulled this stunt if Ukraine still had their weapons.”

“They were afraid to give them up because they thought that’s the only thing that protected them from an expansionist Russia,” Mr. Clinton recalled of Ukrainian views 30 years ago on the Budapest Memorandum. “When it became convenient to him, President Putin broke it, and first took Crimea. And I feel terrible about it because Ukraine is a very important country.”