WARSAW, Poland — A nationalist who is hostile to Poland’s centrist government has eked out a narrow win in a runoff election for the presidency, delivering a severe setback to Prime Minister Donald Tusk, according to official results released Monday.

The winner, Karol Nawrocki, a historian and former boxer who is backed by Poland’s previous governing party, Law and Justice, captured 50.9% of the vote Sunday, adding momentum to a right-wing populist movement in Europe.

President Donald Trump endorsed Nawrocki before the vote.

Nawrocki came out just ahead of Rafal Trzaskowski, the liberal mayor of Warsaw, who was supported by Tusk’s party, Civic Platform. Trzaskowski had 49.1% of the vote.

That outcome leaves Poland bitterly divided with two power centers — the government and the presidency — pulling in opposite directions.

The two sides agree that Poland should provide weapons to Ukraine for its war against Russia and build up its military, but diverge sharply on most domestic issues, including abortion, which was all but banned during eight years under the right-wing Law and Justice government.

The Polish runoff came just two weeks after voters in Romania rejected a nationalist candidate in a presidential election, a result that raised the hopes of Polish liberals that Europe’s right-wing populist wave was receding.

Nawrocki’s win left those hopes shattered and will also disappoint mainstream forces in the European Union, which are aligned with Tusk, a former senior official in Brussels with strongly pro-European views.

The Polish presidency has no say in setting economic or other policy, which are the preserve of Tusk and his ministers, but it has veto power over legislation that allows it to stymie the program of the separately elected government.

Tusk, a veteran centrist, became prime minister in December 2023 after Law and Justice lost its parliamentary majority.

The departing president, Andrzej Duda, like Nawrocki, is an ally of Law and Justice, and frequently vetoed laws passed by Tusk’s majority in parliament or sent them for review by courts stacked with loyalists of the previous government. He was ineligible to run again because of term limits. There is little chance that Nawrocki, a pugnacious novice politician, will wave through laws that had been blocked by Duda.