Despite repeated claims to the contrary, Mayor de Blasio is positioning himself to be the leftist “progressive” alternative to Wall Street-friendly Hillary Rodham Clinton as the Democratic candidate for president, a national party operative told The Post. De Blasio’s hope, the operative said, is a “draft de Blasio’’ movement will develop among progressive activists over the next several months that will lead to the mayor being able to defeat Clinton in the primary elections next year in much the same way leftist Sen. George McGovern successfully challenged the initially front-running establishment Democratic candidate, Sen. Edmund Muskie, more than 40 years...