A federal appeals court ruled Friday that three deputy U.S. marshals who shot and wounded a fleeing teenage driver eight years ago cannot be sued for excessive use of force. The U.S. Court of Appeals for the D.C. Circuit said it was not “clearly established” at the time of the shooting that the deputies violated Michael Fenwick’s constitutional rights when they used deadly force to subdue him. The case in Washington, D.C., unfolded amid a national debate over racially charged incidents of police force in Ferguson, Missouri, and New York City. …