A senior adviser to South Bend, Indiana Mayor Pete Buttigieg’s presidential campaign subtweeted Sen. Kamala Harris (D-CA) for walking back her position on federally mandated busing just after berating former Vice President Joe Biden on the Democratic debate stage last week over the issue.

Buttigieg’s Lis Smith argued in a tweet on Thursday that candidates shouldn’t use debates to “litmus test policies they’re gonna disavow once they get a poll back.”

The story of the 2020 Democratic primary shouldn’t be how individual candidates used debates to deep six rivals and push litmus test policies they’re gonna disavow once they get a poll back. Keep calm, carry on, and win the era! — Lis Smith (@Lis_Smith) July 4, 2019

Harris has been criticized by people in the Biden campaign and pundits alike for walking back her position on busing. When reporters asked Harris on Wednesday whether she thought busing should be federally mandated, she hedged and only opted to say it was a “tool” that could be used to desegregate schools.