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 said on Wednesday it had uncovered what could be an attempt to interfere in its presidential election campaign using advertisements on Facebook that may have been financed from abroad, an assertion the social media platform disputed.