State Rep. Ed Gainey got a humbling message Tuesday night when Mayor Bill Peduto called him to concede the Democratic primary for mayor of Pittsburgh. It was a warning of sorts: You’ve been elected as a grassroots progressive. Now comes the hard part. Peduto knows from experience; he was elected as the progressive candidate in 2013 and, eight years later, the progressive movement in the city coalesced around his rival and ousted him from office. Gainey and Peduto sparred all spring about policing, housing, UPMC and more.