DENVER – Sen. Bernie Sanders’ robust start in the race for the presidential nomination is triggering alarm among congressional Democrats, with many warning that a ticket headed by the self-declared socialist could be devastating to the party’s chances of winning the Senate and holding the House in November. In anxious huddles around the Capitol, apprehensive Democrats are sharing their worries that Sanders’ socialist label and unyielding embrace of controversial proposals like “Medicare for All” and the Green New Deal will repel voters in the affluent, moderate districts that flipped House control in 2018 and in closely divided states where Republican senators are vulnerable. The Vermont independent narrowly won New Hampshire on Tuesday on the heels of a strong showing in Iowa and is widely seen as a front-runner, along with former South Bend, Indiana, Mayor Pete Buttigieg. “I’m a proud capitalist,” said freshman Rep.