CNN  —  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. That could change after a pivotal presidential election, which begins with a first round of voting Sunday. Rafał Trzaskowski, the mayor of capital city Warsaw who is closely aligned with Tusk’s center-left ruling party, is leading opinion polling in the race to replace Andrzej Duda, who has