Aida Amoako in JSTOR Daily:
In the past, hosts like Johnny Carson and Jay Leno avoided taking partisan stances so they wouldn’t alienate half their viewers. Letterman and his successor, Conan O’Brien, did the same for the most part. In more recent years, journalists have discussed what is perceived as an increasing politicization and partisanship of late-night, tracing this phenomenon back to Jon Stewart taking over The Daily Show. Stewart “injected point of view,” writes Bill Carter for CNN. “Late night has not looked back since.”
During the 2004 presidential primaries, most Democratic candidates appeared on shows like: The Jay Leno Show, Letterman, and The Daily Show. According to Variety, politicians made more than 100 appearances on late-night during the 2008 presidential cycle. Obama became the first sitting president to appear on late-night, and Biden has followed his example, appearing on Jimmy Kimmel Live! for his presidential late-night debut.
More here.