Exposing police lying is difficult largely because it is rare for the police to admit their own lies or to acknowledge the lies of other officers. This reluctance derives partly from the code of silence that governs police practice and from the ways in which the system of mass incarceration is structured to reward dishonesty.
Once you've acquired a criminal record, you can be discriminated against legally in employment, housing, and access to education and public benefits. You're relegated to a permanent second-class status, forever a 'criminal.' Inflicting this amount of unnecessary pain and suffering is not cheap.
Perhaps there should be a box on the census form that says, 'I'm a criminal.' Everyone who has ever committed a crime would be required to check it. If everyone were forced to acknowledge their own criminality, maybe we, as a nation, would second-guess our apparent zeal for denying full citizenship to those branded felons.
It is no longer socially permissible to use race, explicitly, as a justification for discrimination, exclusion, and social contempt. So we don't. Rather than rely on race, we use our criminal justice system to label people of color 'criminals' and then engage in all the practices we supposedly left behind.
Bill de Blasio, for his part, became the mayor of New York, surely the most powerful local political position in the nation, and arguably - after Giuliani and Bloomberg - one with a national base, one with, practically speaking, no job at all. He went from marginal political flotsam and jetsam to extraordinary centrality within a few months time.
Running for office, or suggesting you might, is no longer about being a politician but being an independent opinion or sensibility entrepreneur. You're looking for an audience to identify with you. Rather than trying to convince a majority of the electorate, you're looking to cull your particular following.