From the EW interview:
After the 2006 Correspondents’ Dinner [in which Colbert gave a scathing satirical speech about Bush with the President right in front of him, earning some hardcore Beltway backlash], Jon said, ”You touched it. You got close enough to touch it, and it got on you.” Then more than a year passed, and I got kicked off the ballot in South Carolina during my brief presidential run. I had actually been on the phone with people in South Carolina, telling me I was gonna be fine. People were on the phone lying to me. And I called Jon and said, ”I touched it…again.” That was disappointing. I thought I could put myself all the way in it and not feel it, but I did. I realized, ”I understand, maybe, why people end up not being so good.” Because they get lied to a lot.