Three years ago, Moon Jae-in was among the masses on the streets of Seoul seeking to oust a president accused of ignoring the people's will. Now, his own presidency is facing a similar crisis.

Moon was forced to issue a public apology Monday after Cho Kuk, his justice minister and political ally, bowed to a series of mass protests and resigned. The departure represented a stunning setback to Moon, who only five weeks ago had ignored corruption probes swirling around Cho and his family to put him in charge of the country's justice system.

The demonstrations and investigations have only intensified in the intervening weeks, with Cho's home raided by prosecutors and lawmakers shaving their heads to protest the appointment. The conservative opposition — struggling since Moon helped impeach former President Park Geun-hye in 2016 — has climbed level with the ruling Democratic Party in opinion polls.