Prime Minister Shinzo Abe of Japan is planning to sit down with Donald J. Trump in New York on Thursday, in what would be the president-elect’s first meeting with a foreign leader since his election.

Why are they meeting?

Mr. Abe wants to find out how serious Mr. Trump was during his campaign when he repeatedly criticized Japan on trade issues and for not paying more of the cost of its own defense.

And since the Japanese establishment was expecting Hillary Clinton to win the presidency, Mr. Abe wants to assure Mr. Trump that he is willing and eager to work with him.

What is Mr. Abe most worried about?

The prime minister is concerned about Mr. Trump’s commitment to protecting Japan.

The United States is Japan’s most important ally, and is legally obligated to defend it against attack. There are around 50,000 American troops stationed in Japan, a powerful deterrent against the rising threat of North Korea, and an increasingly assertive China.