WASHINGTON — The U.S. Supreme Court ruled today that a New Jersey police officer who was demoted after his boss mistakenly believed he was involved in a political campaign can still bring a lawsuit alleging a violation of free speech rights.The 6-2 ruling said Jeffrey Heffernan could file a First Amendment claim against the city of Paterson, N.J., even if he wasn’t actually taking sides in the local mayoral race.Heffernan claimed he was a victim of retaliation after other officers saw him picking up a campaign …