Former Maryland Governor and Baltimore Mayor Martin O’Malley has joined the 2016 US presidential race, challenging Hillary Clinton and Bernie Sanders for the Democratic nomination.

He highlights his record as a social liberal – citing action on tackling income inequality by raising the state’s minimum wage , legalising gay marriage and helping undocumented migrants gain access to education.

But critics say his “zero-tolerance” policies on crime damaged police-community relations.

Baltimore was rocked in recent weeks by riots over the death of Freddie Gray, a young black man, from injuries sustained while in police custody.