O'Malley expected to announce presidential bid; posts video of himself playing 'Hail to the Chief'

A big announcement is expected Saturday by former Baltimore mayor and Maryland governor Martin O'Malley.

O'Malley is expected to jump into the race for the White House.

His probable announcement is significant because, as a democrat, O'Malley would be the first to challenge Hillary Clinton for the presidential nomination.

On Friday, O'Malley released a video of himself playing 'Hail to the Chief' on the guitar – a teaser to what is expected to be his formal announcement on Saturday.

O'Malley has maintained an active social media presence. He has traveled to Iowa and will head to New Hampshire – two key states in the early presidential primaries.

Some Baltimore police accountability activists say they'll protest former O'Malley's announcement of a possible presidential bid in the city Saturday morning.

Duane Davis of Baltimore Bloc said Thursday that police brutality flourished under O'Malley's "zero-tolerance" law enforcement policies during his seven years as mayor. Davis traces the death of Freddie Gray, who suffered a fatal injury in police custody, to O'Malley's policies.

The Associated Press contributed to this report.