BUDAPEST, Hungary (AP) — Hungarians were casting ballots Sunday in what is widely seen as Europe’s most consequential election this year, a vote that could unseat populist Prime Minister Viktor Orbán, an ally of U.S. President Donald Trump, after 16 years in power.

It’s a key moment for Orbán, the European Union’s longest-serving leader and one of its biggest antagonists, who has traveled a long road from his early days as a liberal, anti-Soviet firebrand to the Russia-friendly nationalist admired today by the global far-right.

Orbán has frustrated and even alarmed many leaders across the European Union with what they view as his steady drift away from Western partners and toward Russian President Vladimir Putin. Recent revelations have shown a top member of his government frequently shared the contents of EU discussions with Moscow, raising accusations that Hungary was acting on Russia’s behalf within the bloc.

Polls opened at 6 a.m. and were scheduled to close at 7 p.m. Orbán and his top challenger, Péter Magyar, arrived at separate polling stations in Budapest at nearly the same time to cast their votes.

Speaking to reporters outside, Orbán, 62, said the campaign had been “a great national moment on our side” and thanked activists and supporters for their work. “I’m here to win,” he said.