Biden nominates ex-Maryland governor Martin O'Malley to lead Social Security Administration

O'Malley served as governor of Maryland from 2007-2015 and ran for president in 2016.
Appointment requires Senate confirmation and may face Republican scrutiny.
O'Malley would oversee an agency facing management and financial challenges.
Biden has vowed to strengthen Social Security after firing previous commissioner.
O'Malley praised by Biden for public service record and commitment to accessible government.