Every commander-in-chief has one mission above any other: keeping our country safe.

Rhode Islanders are fortunate to be represented by one of our nation’s most distinguished leaders on national security, Sen. Jack Reed. I’ll never forget spending Thanksgiving with Senator Reed and our troops at Bagram Air Base, in Afghanistan, in 2003. Watching Jack with the brave men and women who put their lives on the line for our country, and working with him in the Senate, I was reminded that a true leader has to have the right temperament, experience and judgment, and set an example that reflects the best values of our nation.

That’s one reason so many Americans are alarmed by what we’re hearing on the campaign trail this year. Bluster and bigotry don’t make candidates sound tough — it makes them sound in over their head. And Donald Trump, in particular, has made some of the most reckless statements on national security in the modern history of presidential campaigns.

Mr. Trump’s views are not just wrong — they’re dangerous. And they fly in the face of years of bipartisan consensus.

When he talks casually about letting more countries develop nuclear weapons — even friendly ones — that means that more of these dangerous arms will exist around the world. It’s not hard to imagine this proliferation setting off arms races in volatile regions like East Asia and the Middle East, increasing the chance that some of these weapons might fall into the wrong hands.

Terrorists are already anxious to acquire weapons of mass destruction. For instance, we recently learned that the attackers in Brussels had been actively monitoring Belgian nuclear power facilities and personnel. And we can be sure that they would never hesitate to use a dirty bomb.

That’s what’s at stake in this election. Our next president must be ready to confront this threat, not make things worse.

I represented New York in the Senate during the 9/11 attacks. That experience led me to introduce the Dirty Bomb Prevention Act, which would have made it harder for terrorists to get their hands on radioactive material.

As secretary of state, I helped President Obama convince countries like Russia to reduce their stockpiles of nuclear material. And I helped put some of the toughest-ever sanctions on Iran, which ultimately brought them to the negotiating table, and led to a historic agreement to put a lid on their nuclear program.

If I’m fortunate enough to serve as president, I have a clear plan to ensure that America remains safe from these types of threats.

First, we’ll redouble our efforts to lock down our nuclear weapons and protect radioactive materials against theft. That means investing in new technologies to upgrade antiquated security systems, and helping federal, state and local authorities coordinate their efforts more effectively.

Second, we’ll crack down on any attempts to illegally transport radioactive material by improving our border security, and strengthening our export controls.

And third, we will continue our ongoing goal of reducing the amount of nuclear material that exists around the world. We should help other nuclear nations use less weapons-grade material for their civilian power systems, and negotiate a global moratorium on the creation of any more of it — because the world already has more than enough.

I believe that weapons of mass destruction ending up in the possession of terrorists willing and eager to use them is the most serious security threat facing America.

And that’s just one of the many complex problems and hard choices our next president will confront in the Oval Office. He or she will sit down and start making decisions that will affect the lives and livelihoods of every American, and people all over the world.

I’ve worked closely with many foreign leaders, and I know many of them are alarmed by the rhetoric they’re hearing. They wonder if the America they know — the America that leads the world, that is strong and smart and principled — might be at risk of disappearing.

So our choice is clear. We can remain the indispensable nation that mobilizes common action on a global scale. Or we can abandon our longstanding principles and start treating foreign policy like a game.

Some risks we can’t afford to take.

Hillary Clinton is a Democratic candidate for president and a former U.S. secretary of state.