<p>BOSTON —Standing in front of a cheering crowd of 800 construction trade union members and supporters inside Boston’s historic Faneuil Hall with Mayor Marty Walsh by her side, Hillary Clinton turned Sunday to a subject that she hasn’t devoted much time to on the campaign trail: pothole politics.</p><p>At an event billed as “Hard Hats for Hillary,” Clinton unveiled a $275 billion infrastructure proposal to fix highways, trains, airports, aging sewer systems and the country’s frayed electrical grid.</p><p>“Here in Boston, I remember the historic snowfall you had last winter,” she told the packed hall, where an overflow crowd of about 1,200 supporters watched on a screen set up in the square outside.