THE CHEERS at Rafal Trzaskowski’s election party on May 18th sounded unconvincing. So was his margin of victory. The liberal mayor of Warsaw came away with 31.4% of the vote in the first round of Poland’s presidential election, compared with 29.5% for his main rival, Karol Nawrocki, the candidate of the nationalist Law and Justice (PiS) party. Mr Trzaskowski, backed by Poland’s prime minister, Donald Tusk, and his centrist Civic Coalition (KO), had long been the front-runner. Ahead of the run-off, scheduled for June 1st, the tables have turned.