The voters have spoken, and Donald J. Trump will be the 47th president of the United States. With a Republican-controlled Senate and strong backing in the House, Trump will be in position to implement his agenda, starting in January. What does that mean for foreign policy?

It’s hard to say with certainty. In Trump’s first term, from 2017 to 2021, foreign policy was marked by chaos and disputes with our allies. He has promised more of the same: tariffs, confrontations and a go-it-alone approach to dealing with friends and enemies.

But Trump is unpredictable. We can count on surprises.

One of the most urgent questions is, what will happen with Ukraine? Since Russia invaded in February 2022, the U.S. has been Ukraine’s staunch supporter. Trump has praised Russian leader Vladimir Putin and criticized U.S. policy. He claimed Russia wouldn’t have invaded if he were president and boasted that he could end the war in 24 hours. Ukrainians are right to be worried.

Another crucial issue is U.S. involvement in NATO. Trump has railed against the organization, threatening, when he was president, to pull back support for the world’s most successful military alliance and the most important check on Russian aggression. President Biden made America a reliable NATO partner. Trump may upend that stance.

In the Middle East, combine Trump’s unpredictability with the volatility on the ground, and it’s anyone’s guess what will happen. Israeli Prime Minister Benjamin Netanyahu welcomed Trump’s election, believing he will be more supportive of Israel and more hostile to Iran than Biden. But what that will look like defies guesswork.

The cornerstone of Trump’s foreign policy, according to his campaign promises, will be to impose steep import tariffs, especially on China and Mexico. Trump says tariffs will pay for his proposed tax cuts and help U.S. manufacturing. But economists say tariffs provoke trade wars, raise prices for consumers and damage the economy.

Of course, Trump won’t necessarily get everything he wants. In his first term, for example, he vowed to build a border wall and make Mexico pay for it. That didn’t happen. When he imposed tariffs, other countries responded in kind, causing some U.S. exports to plummet.

But Trump’s “America First” approach did mark a real change. He angered many of our traditional allies, especially in Europe, and played nice with our adversaries.

He withdrew from the Paris climate accord, the Iran nuclear deal and several arms control pacts. Biden brought the U.S. back into the climate agreement, but Trump says he will leave it again.

Trump has expressed admiration for autocrats like Putin, China’s Xi Jinping and Hungary’s Viktor Orban, who suppress dissent and scorn democracy. That worries advocates for human rights and the rule of law. Trump has promised the “largest deportation program in American history”, removing millions of immigrants from the U.S. Such a move would be incredibly costly and could cause chaos in Latin America and the Caribbean region.

One of Trump’s most worrisome plans is to fire thousands of career government employees and replace them with political appointees. This would be especially damaging at the State Department, where experienced and dedicated diplomats and regional experts are essential for representing America’s interests.

Trump values loyalty to himself above all else. With his transactional outlook, he casts every relationship as a “deal” in which there will be winners and losers. Supporters say his unpredictability is a feature, not a bug.

It keeps opponents guessing. The approach may work in business, but it’s not suited to governing.

Effective foreign policy requires looking out for our national interests while incorporating American values, including democratic decision-making, human rights and individual dignity. It takes reliability and consistency: Allies and adversaries need to know we mean what we say and will keep our promises.

With a second Trump presidency, we can hope for the best, but there will be no guarantees.

—Lee Hamilton is a distinguished scholar at the IU Hamilton Lugar School of Global and International Studies and senior advisor for the Indiana University Center on Representative Government. He was a member of the U.S. House of Representatives for 34 years.