He wasn't really trying before. It was a joke. To me activities like the RSA speaking are political activities. And they do not simply represent Colbert's personal views. This is probably the extreme edge of the leftish faction that still has influence and is connected to power. It is extremely critical of existing power and yet stays within "mainstream" parameters. If that group can see a realistic path towards political office that would provide more influence than the TV show and is likely to succeed in Colbert's person then he will be encouraged and quite possibly actually pursue a political office. That's my outsiders guesstimate of this.