After a bullet was fired at Donald J. Trump during a campaign rally in Pennsylvania in July last year, President Mahmoud Abbas of the Palestinian Authority sent him a letter denouncing the violence.

Mr. Trump posted his ebullient response on social media: “Mahmoud — So nice — Thank you — Everything will be good.”

But little is good between Palestinian officials and the Trump administration. Last week, the United States, a staunch supporter of Israel, blocked U.S. visas for Mr. Abbas and his staff, preventing them from attending the annual meeting of the United Nations General Assembly later this month.

Several countries, including France and Canada, plan to use the occasion of the assembly to declare their recognition of a Palestinian state, and a conference focused on recognition of Palestinian statehood is scheduled to take place on the sidelines of the gathering.

Recognition of a Palestinian state does not mean that oneis closer to being established. But the move by these countries carries significant symbolic weight as Israel finds itself ever more isolated internationally over the war in Gaza, in which tens of thousands of Palestinians have been killed.

For Mr. Abbas, the conference would have been an opportunity to revel in the moment on an international stage. Now, he is launching a diplomatic blitz to try and reverse the American decision to bar him.