Democratic presidential candidate Martin O’Malley thanked Republican South Carolina governor Nikki Haley for removing the Confederate flag from the South Carolina state house.

O’Malley made his remark during his opening statement at the Democratic debate, hosted by the Congressional Black Caucus Institute in Charleston, South Carolina.

All three candidates opened with remarks about Martin Luther King, Jr., whose national holiday falls on Monday.

O’Malley’s “hat tip” to Nikki Haley quickly garnered the notice of Twitter.

Nikki Haley’s decision to bash Donald Trump in her GOP response to the State of the Union inflamed tensions within the Republican Party and led to criticism of Haley for being left-wing.