Hillary Clinton ally David Brock on Monday resigned from the board of a pro-Clinton super-PAC, according to a letter obtained by Politico, accusing it of leaking information about other pro-Clinton groups. The move is a sign of fighting among the network of pro-Clinton groups, the kind of strife that plagued the Clinton campaign in 2008 but that allies were trying to avoid this time around. Brock is resigning from the board of Priorities USA Action, and his letter claims that officials there leaked information to The New York Times about the fundraising practices of two pro-Clinton groups founded by Brock:...