Lee said Mirkarimi's return to office tarnishes the city's nationally recognized programs designed to combat domestic violence.
"Domestic violence has been a bulwark, a very strong principally held policy for this city that we do not tolerate," the mayor said.
One of Mirkarimi's attorneys, Shepard Kopp, said Wednesday that it appears Lee and Gascon did not hear what the board said during Tuesday's hearing. "Almost every one of them said that no matter the vote, the city needed to come together and move past this unsettling course of events," Kopp said.
San Francisco's sheriff does not have broad law enforcement powers as sheriffs do in other jurisdictions. The position mostly entails overseeing an organization of more than 800 sworn officers and a civilian staff of about 100.
The department runs San Francisco's jails with an average daily inmate population of 2,200, provides City Hall and courtroom security, carries out court-ordered evictions and warrants, and aids San Francisco police in enforcement actions.
The case unfolded from a Dec. 31 argument between Mirkarimi and Lopez, over whether she could travel to her native Venezuela with their toddler son. During the dispute, Mirkarimi grabbed and bruised Lopez's arm. Lopez turned to a neighbor who later contacted police after videotaping Lopez's tearful account of the incident.
The four supervisors said that while they agree domestic violence is a serious matter, each felt that Mirkarimi's behavior was not official misconduct under the city's charter. They also thought that his removal could make it too easy to oust other duly elected officials in the future.
"We must interpret this provision (of official misconduct) narrowly or open the door, open the door wide for potential abuse," Supervisor David Campos said before his vote.
Anti-domestic violence groups, which had called for Mirkarimi to step aside, were crestfallen and angered by the vote Tuesday.
"I think they are wrong," said Kathy Black, executive director of La Casa de las Madres. "It sends a terrible message that domestic violence is not a serious problem and that we don't take it seriously in San Francisco.
"We deserve a law enforcement official who meets the highest standards."