Since President Trump returned to the White House this year, President Volodymyr Zelensky of Ukraine has stuck to one rule: Never miss a chance to meet with the U.S. leader to try to pull him into Kyiv’s corner. Mr. Zelensky will meet with Mr. Trump on the sidelines of the United Nations General Assembly in New York, Karoline Leavitt, the White House press secretary, told reporters on Monday. For Mr. Zelensky, a sit-down with Mr. Trump could deliver more results than his speech to the General Assembly, a forum where Russia’s full-scale invasion of Ukraine has gradually slipped down the agenda after more than three years of war. The last time the two leaders met, at the White House last month, Mr. Zelensky came away with a win. He secured a U.S. commitment to participate in security guarantees for Ukraine as part of a peace deal aimed at deterring future Russian attacks.