JERUSALEM — Prime Minister Benjamin Netanyahu of Israel, in the middle of a re-election campaign, seemed set to score back-to-back diplomatic triumphs in a span of just a few days, with Poland, of all countries, playing an important role in both.

This past week, Mr. Netanyahu attended a meeting in Warsaw, convened by the Trump administration, where five dozen nations discussed the common strategic threat posed by Iran.

Sunni Arab nations were also at the conference, and Mr. Netanyahu made the most of it, appearing behind closed doors alongside diplomats from Saudi Arabia, Yemen and Bahrain and later leaking a video in which Bahraini and Saudi officials could be heard echoing his frequent warnings that Iran is the Middle East’s greatest danger.

And in Jerusalem on Monday night, Mr. Netanyahu had planned to welcome the leaders of Poland and three other East European countries whose support he has cultivated as a way to push back against interference by what they all perceive, to varying degrees, to be another common adversary: the European Union.