WARSAW (Reuters) -Polish President Karol Nawrocki took part in a teleconference on Ukraine with U.S. President Donald Trump and European leaders on Wednesday, his office said, a call his bitter political rival Prime Minister Donald Tusk had been expected to attend.

The election victory of Nawrocki, who was backed by the nationalist opposition party Law and Justice (PiS), dealt a blow to Prime Minister Donald Tusk’s hopes of cementing the pro-European Union course he has set for the bloc’s largest eastern member and left his government floundering in the polls.

Conservative Karol Nawrocki was inaugurated Wednesday as Poland 's new president, which could set the country on a more nationalist course.