Republican presidential candidate Donald J. Trump has not ruled out using a nuclear bomb once he becomes president. As he told interviewer Chris Matthews in late March, “I’m not going to take it off the table.” Nor would Trump object if South Korea and Japan acquired nuclear weapons. If they did so, he said, the U.S. “may very well be better off.”

It has long been U.S. policy to oppose the development of such a bomb by any other country, including our allies. The aim is to prevent the proliferation of nuclear weapons and make sure they would not be acquired by a rogue state. So far this policy has worked; the spread of nuclear weapons has been limited, if not entirely prevented. There is good reason for calling the use of a nuclear weapon “unthinkable.” In August 1945, two atom bombs dropped by the U.S. all but obliterated the Japanese cities of Hiroshima and Nagasaki. Today the U.S. and Russia possess nuclear weapons with many times the destructive power of the earlier bombs. If a nuclear exchange ever took place, the destruction would be greater than anything the world has ever known, and much of the earth would be contaminated by fall-out.

President Obama until recently seemed fully aware of the danger of nuclear proliferation. He was awarded the Nobel Prize for peace in 2009 after he called for a nuclear-free world. The Nobel Prize committee also cited a speech he made in which he pledged to “reduce the role of nuclear weapons in our national security strategy.” But instead of following through on those promises, Obama is taking actions that assure the resumption of a nuclear arms race. Administration plans now call for the U.S. to spend a trillion dollars over the next three decades modernizing its nuclear arsenal. In mid-May the Pentagon announced that it was updating its atom bombs to make them more accurate and to “minimize collateral damage.” The recently unveiled B61 is the first of five new warhead types called for in the updating of America’s nuclear weapons.

Among its other advantages is its smaller size, with less fallout on detonation. “What going smaller does is to make the weapon more thinkable,” said Gen. James Cartwright, former vice chairman of the Joint Chiefs of Staff. Critics agree, saying that’s just what’s wrong. The improvements will make nuclear weapons more usable — even in a first strike.
As if such developments were not enough to concern the Russians, U.S. and allied officials recently celebrated the opening of a new, reinforced missile defense  system in Romania, at the Deveselu air base, as well as a second missile defense site in Poland scheduled for 2018. The U.S. insists the system is aimed only against “rogue states” such as Iran, and not Russia, a claim that meets with skepticism in Russia. The Russians are aware that so-called defensive weapons are weapons that make an offensive strike safer to carry out by protecting against retaliation.

According to a Russian Foreign Ministry spokesperson, “We still view the destructive actions of the United States and its allies in the area of missile defense as a direct threat to global and regional security.” The Russians accuse the U.S. of violating the Intermediate-Range Nuclear Forces Treaty of 1987, which banned land-based cruise and medium-range missiles with a range between 300 and 3,400 miles.

Russian president Vladimir Putin has threatened to withdraw from the treaty entirely, and go ahead with deployment of a nucleararmed drone submarine that would operate in coastal waters and could set off catastrophic tsunamis and floods. It is not necessary to admire Putin to have sympathy for his position. NATO has steadily moved eastward under Bush and Obama, so that today its troops are stationed on Russia’s borders.

The good news is that Trump says he opposed the war in Iraq and as president would refrain from foreign interventions. The bad news is that Trump easily changes his mind, one day saying he would bar all Muslim immigrants from entering the U.S., the next day saying he didn’t mean all Muslims. In any case he would come to the presidency with no political experience, and with no evident knowledge either of international law or of history. We as yet have no idea who his foreign policy advisers are, and can only hope they are not the same ones who advised George W. Bush to invade Iraq.

Peter Wehner, a former director of the White House Office of Strategic Initiatives under Bush, was recently quoted in the New York Times as saying of Trump, “I consider him to be a malicious and malignant figure on the American political landscape — cruel, vindictive, obsessive, narcissistic, a nativist and xenophobic…” Even if Wehner is guilty of overstatement, the fact that an individual with Trump’s shortcomings could someday have his hand on the nuclear button is alarming. If deploying a nuclear bomb is unthinkable, only a little less unthinkable is a President Trump in the White House.

Rachelle Marshall is a former editor and writer and a member of Mill Valley Seniors for Peace, a Jewish Voice for Peace, and Women’s International League for Peace and Freedom.