But European leaders whose countries are members of the NATO alliance are also deeply concerned about how Mr. Trump may act during their two-day summit meeting on July 11-12, fearing the consequences of a divisive meeting just days before the president is expected to hold talks with the Russian president, Vladimir V. Putin.

This month, citing “national security,” Mr. Trump imposed tariffs on imports of European steel and aluminum. The bloc responded with “rebalancing measures” that hit about $3.25 billion worth of American products, a rough equivalent to the value of the penalties on European steel and aluminum.

The European Union is currently preparing similar retaliation should Mr. Trump follow through on his threat to impose significant new tariffs on imported automobiles.

In a briefing before the summit meeting, the French economy minister, Bruno Le Maire, said in Paris that “we do not want a trade war.”

“But we defend ourselves,” he added. “No one can stop a person or a state that is attacked from defending himself. We are attacked; we are not the aggressors.”

For now, migration is the highest priority for the leaders, with Chancellor Angela Merkel of Germany pressed by rivals in her own coalition government to find a way to deal with migrants who register in another country before they try to settle in Germany. That is part of a phenomenon known as secondary or onward migration, made possible by what is essentially border-free travel through much of Europe within what is known as the Schengen area.

Although migrant numbers are down, the politics around the issue have propelled populist parties to success across Europe, including in Italy and in Germany, where the Alternative for Germany is the official opposition party.