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Stephen Colbert drops the act to help his sister

Colbert Busch is the heavy favorite to win Tuesday's Democratic primary for the seat, while Republicans are likely to have a runoff between controversial former South Carolina Gov. Mark Sanford (R) and a second-place finisher. She faces an uphill race in the GOP-leaning district, but has run a strong campaign so far.

"If people think that's not the right thing for me to do, I don't care," Colbert said. "It's my sister and I'm willing to help her."