To preserve his ego, the O'Reilly Factor host called his rival Limbaugh a "straw man" who "nobody takes seriously" as the purported head of the Republican party. He also claimed personal credit for the right-wing radio host's recent ratings surge (since O'Reilly recently ended his own radio show).
Beck apparently emerged unscathed. O'Reilly will presumably leave his rising-star, Fox News colleague to the likes of Dennis Miller and Shep Smith.
There's no sign yet that Letterman asked O'Reilly about his producers' stalking and ambush of ThinkProgress' Amanda Terkel.
A quick excerpt of O'Reilly's appearance is above, taken from the longer YouTube outtake below.