"As a broadcast journalist, I'm obligated to maintain pure objectivity," he said on the show. "It doesn't matter that my sister is intelligent, hard-working, compassionate and dedicated to the people of South Carolina. I will not be mentioning any of that on my show."
Stephen Colbert will host campaign fundraiser for his sister
Colbert joked about his sister's candidacy on the show shortly after she announced — though he'd promised to stay neutral.