A Sister Souljah Moment

Bill Clinton, running for president in 1992, criticized a black performer called Sister Souljah who had said some racially antagonistic and violent things about whites. Therein was born the term "Sister Souljah moment" which is defined by Wikipedia as follows:

In United States politics, a Sister Souljah moment is a politician's public repudiation of an allegedly extremist person or group, statement, or position perceived to have some association with the politician or their party.

President Barack Obama, who was strongly supported for election by the teachers' unions, has supported the firing of all the teachers at a poorly performing school in Rhode Island. This may be Obama's Sister Souljah moment, see this article from The Washington Post.