Poles awakened Monday to a clear albeit close result that returns a nationalist politician to the presidency who has pledged to hinder the centrist, pro-EU government for the remainder of its term.

Karol Nawrocki, a historian and former boxer, will be Poland’s next president. Nationalist forces in the United States and Europe had been rooting for him: Mr. Nawrocki was supported by President Trump, Prime Minister Viktor Orban of Hungary and George Simion, a right-wing politician in Romania who recently lost a presidential election.

Karol Nawrocki, a populist conservative backed by U.S. President Donald Trump, has won Poland's presidential runoff election, according to official results released Monday. Eyes across the country, Europe and even North America were watching the race in Poland,