The Federal Election Commission has dismissed Republican accusations that Twitter violated election laws in October by blocking people from posting links to an unsubstantiated New York Post article about Joseph R. Biden Jr.’s son Hunter Biden, in a decision that is likely to set a precedent for future cases involving social media sites and federal campaigns. The F.E.C. determined that Twitter’s actions regarding the Hunter Biden article had been undertaken for a valid commercial reason, not a political purpose, and were thus allowable, according to a document outlining the decision obtained by The New York Times. The commission’s ruling, which...