President-elect Joe Biden is expected to take a historic step and select a woman to head the Pentagon for the first time, shattering one of the few remaining barriers to women in the department and the presidential Cabinet. Michele Flournoy, a politically moderate Pentagon veteran, is regarded by U.S. officials and political insiders as a top choice for the position. The most recent defense secretary to go was Mark Esper, who was fired by Trump on Monday after pushing back on issues including troop withdrawals and the use of the military to quell civilian unrest.