Well, now I'm really thinking about it, and look: this may require its own thread somewhere else.
But wasn't the republican party a shitshow during the 2nd George W. Bush presidency? And just in general, during the post-Bush presidencies, you had the Tea Party movement, Sarah Palin saying stupid shit, Romney being useless and letting democrats call him a nazi with a smile on his face, etc. - the era of being a "gracious loser" and all that. Before Trump finally decided to get into politics.
I'm thinking Stewart (and his team of writers) got way too used to the republicans being a punching bag. It was too easy for too long. He fucked off from Comedy Central by August 2015 and by then, the damage was done. I knew numerous young adults who mainly got their political takes from the Daily Show and The Colbert Report (which had also ended by 2014). The latter had shown some ugly cracks towards the end, with Colbert giggling along with Anita Sarkeesian...
Anyways, now, it's not that easy anymore in the sense that the dems have become a cult. And I've seen redditors get mad when he dared to criticize them since returning to the Daily Show, even though it's small potatoes compared to how he went after the republicans. They accuse him of both-sides-ism or whatever term they used to shit on him, in threads I saw.