Since winning power back from the hands of his populist rivals a year and a half ago, Poland’s Prime Minister Donald Tusk has faced one very stubborn roadblock to his plans: the country’s president.

Power in Poland rests primarily with the prime minister and parliament. But the president wields real influence by signing laws into force, or vetoing them, appointing judges and ambassadors, and helping to shape foreign policy. Presidents can rarely impose their own agenda, but they can certainly frustrate the government’s.

Poland holds a presidential election on Sunday as the conservative incumbent Andrzej Duda nears the end of his second and final term.