Immigration is a topic that has been covered on The Colbert Report recently, although not in great depth. In August, Colbert spent a day working on a vegetable farm in New York, alongside many migrant field workers. Apparently this experience qualifies him to testify before Congress.
Colbert managed to sneak a lot of jokes into his testimony (including saying that he wants to submit video of his colonoscopy into the Congressional Record), but he did get real for a few moments. He said that he feels a need to talk about people who are powerless on his show.
Here’s the video: