Last month, Trump said Orbán had his “complete and total support” in a video message to the Hungarian Conservative Political Action Conference (CPAC) in Budapest.

On Sunday Orbán faces Péter Magyar, a former insider in the prime minister’s Fidesz party, who broke with him two years ago to found the centre-right Tisza party.

Tisza leads Fidesz by between 10% and 20% in most polls. Only the strongly pro-government Nézőpont agency puts Fidesz narrowly ahead.