EU leaders gather for summit in Brussels

German political parties have been in talks since last month's election to form a ruling coalition and if they succeed by mid-December, the 67-year-old Merkel will not return to Brussels as chancellor after 16 years and over 100 summits.

Long-running tensions between Poland's ruling nationalists and the bloc's liberal majority have risen sharply since Poland's Constitutional Tribunal ruled on Oct. 7 that elements of EU law were incompatible with the country's charter.

In challenging a central tenet of EU integration the case risks precipitating a new fundamental crisis for the bloc - still grappling with the after-effects of Brexit - as well as Poland losing generous European handouts.