Police and protesters clashed outside Democratic National Committee headquarters on Wednesday night during a demonstration for a cease-fire in the war between Israel and Hamas, the latest reflection of boiling tensions over the bloody conflict. Scores of Democratic representatives and candidates, including House Minority Leader Hakeem Jeffries, were inside the building for a campaign reception when it was interrupted by chanting outside. Protesters said they wanted to block entrances and exits to force politicians to encounter their candlelight vigil and their calls for an end to the fighting.