"America deserves to know if his show was canceled for political reasons," Sen. Elizabeth Warren, D-Mass., said.

When it was announced in 2014 that Stephen Colbert would succeed David Letterman as host of the CBS “Late Show,” reaction was mixed. Letterman, who retired after helming the talk show for 22 years, had a loyal audience. At that point, Colbert was best known for playing a satirical version of himself on Comedy Central’s “The Colbert Report.”