When the open housing proposal became public, local reaction was often hostile. Such was the reaction of many residents in Warren, Michigan, a predominately white blue-collar suburb of Detroit. While it had no formal discriminatory laws, most blacks were excluded by zoning practices, refusals to sell to them, and intimidatory actions of white property owners, many of whom were ethnic Polish and Catholic and had moved to the suburb as part of white flight. By this time, Detroit was 40–50 percent black. HUD made Warren a prime target for Open Communities enforcement and threatened to halt all federal assistance to the town unless it took a series of actions to end racial discrimination there; town officials said progress was being made and that their citizens resented forced integration. Romney rejected this response, partly because when he was governor, Warren residents had thrown rocks and garbage and yelled obscenities for days at a biracial couple who moved into town. Now the secretary said, "The youth of this nation, the minorities of this nation, the discriminated of this nation are not going to wait for 'nature to take its course.' What is really at issue here is responsibility – moral responsibility."