Writing at The Federalist, David Marcus cites several examples of Donald Trump - while developing real estate, building hotels, and running casinos - doing business with known mobsters in Atlantic City and New York City. As Marcus notes, it is time for serious investigative reporting about these disqualifying ties.
Trump's poll numbers require the press take him seriously and vet him. Likely he will claim, probably truthfully, that anyone doing what he has done in the cities in which he operated would end up working with the mob to some extent.
Having done so is no problem for Trump, the celebrity impresario. It is a problem for Trump, the presidential candidate.