Nuclear war has been unthinkable for decades. Not anymore.

Nuclear weapons are back in vogue.

Ah, the fond memories: the 1984 TV movie The Day After, the nuclear freeze campaign, the B-1 bomber debate, the M-X missile fight.

Don’t remember these seminal events? In a national-security era dominated by fear of terrorism, a substantial part of the American population has either forgotten, or never knew, that national-security arguments from the 1950s-80s were dominated by the fear there might be a nuclear war.

The Bulletin of the Atomic Scientists, a journal created by many of the brains that brought the world nuclear weapons to begin with, indexed the proximity of nuclear war every year by setting its “doomsday clock” – so many minutes to midnight. The clock continues to tick. It is three minutes to midnight.

The end of the Cold War pushed nuclear issues into the background for more than 25 years. Yet the weapons, even in reduced numbers, remained. Oh, there were some pretty major nuclear side-shows: Saddam Hussein, we were told, had a nuclear capability. (He didn’t.) Iran was rushing toward such a capability and would never stop. (They did.) But the big one, the fear of a U.S.-Russia nuclear armageddon, had receded into the past.

Just when you thought it was safe to go out, the whole nuclear dilemma has tumbled back onto the table. Once again, we are thinking the unthinkable. The Russians are said to be “aggressively” expanding their nuclear arsenal, while the Americans start a trillion-dollar nuclear modernization program of their own.

The Chinese, not to be outdone, modernize their own strategic weapons, and North Korea announces it will test a strategic missile capable of striking the U.S. Meanwhile, India, whose nuclear test led to the creation of Nuclear Suppliers Group to prevent the spread of nuclear technologies – and which has not signed the non-proliferation treaty – wants to join that group.

Russia’s Vladimir Putin declares “it’s best not to mess with us,” adding “I want to remind you that Russia is one of the leading nuclear powers.”

Not missing a beat, Donald Trump responds in kind: “Let it be an arms race. We will outmatch them at every pass and outlast them all.”

Supporters of the trillion-dollar U.S. nuclear modernization program, found in the Pentagon, the Energy Department’s National Nuclear Security Administration, Los Alamos and Lawrence Livermore, are, no doubt, delighted at this turn of events.

It’s not that the U.S. does not have enough nuclear weapons; we have more than enough. The answer to the nuclear dilemma is political, not military. It involves reassurance on all sides about intentions and capabilities; renewed negotiations to limit the expansion of nuclear programs; and a recognition that stability is in the interests of both Russia and the U.S.

I hold out no fond hopes that such logic will prevail over the next four years, but one never knows; lightning could strike.

GORDON ADAMS is a distinguished fellow at the Stimson Center. From 1983-87, he was the senior White House official for national security.