A historian and populist firebrand who boasted about his brawls with soccer hooligans has narrowly won Poland’s presidential election, in a political upset that could torpedo the centrist government’s efforts to unspool the legacy of authoritarianism in the country.

Nawrocki, an admirer of President Donald Trump, won 50.89% of votes while Trzaskowski clinched 49.11%, according to The Associated Press. His election is seen as a victory for Trump and his administration, who made it clear that Nawrocki was their preferred candidate.

WARSAW—Exit polls in Poland’s presidential election predicted a slim victory for a conservative historian who had been given a nod of support by President Trump and is a backer of the former ruling Law and Justice party,

Poland's path to narrowing its fiscal deficit, maintaining its credit ratings and keeping investors on board looks more difficult following conservative nationalist Karol Nawrocki's presidential election triumph.

Rafał Trzaskowski, from Prime Minister Donald Tusk’s centre-right party, is on course for run-off victory over rightwing rival

A runoff election on Sunday pits a centrist against a nationalist who represent mainstream parties. The outcome is unclear given that many under 30 prefer candidates on the political fringes.

Poland was voting on Sunday in a tight presidential election that will determine whether the country cements its place in the mainstream of the European Union or turns toward Donald Trump-style nationalism.