" but I suspect that's not the way politics were argued back in the Founders' days."

You suspect wrong:

"But don’t think the candidates weren’t playing a central behind-the-scenes role in their campaigns. Jefferson contacted one of his supporters, pamphleteer James Callender, to print a series of vicious tracts spreading lies about Adams. Callender’s publications alleged that Adams planned on going to war with France and that he had a “hermaphroditical character, which has neither the force of a man, nor the gentleness and sensibility of a woman.” Callender’s slanderous attacks damaged Adams’ credibility and helped Jefferson win the election." - http://listverse.com/2014/01/18/10-worst-dirty-tricks-in-american-politics/

I will say this though, Trump is not a creation of Jon Stewart. He's a creation of the Tea Party and our celebrity culture. The Tea Party has been spreading hateful rhetoric since Obama was elected, and Trump used his celebrity status to get attention and take that rhetoric to the next level knowing the Tea Partiers would love it.

Furthermore, it is literally comedians' jobs to poke fun. They are meant to make us laugh, not closely examine the issues... which brings us to the OTHER big failure that's hurting politics today: The real journalists aren't doing their jobs very well. Shows like Jon's often do a better job of journalism than the real television journalists. When you've got a huge percentage of Americans watching what is essentially a propaganda channel for their news, real harm is done... far more than any harm caused by pointing out Trump's tiny hands.

In fact, many have pointed out that Trump received more airtime than any other candidate, by far, on the major news channels. Why? Look no further than the CEO of CBS, Les Moonves:

it may not be good for America, but it’s damn good for CBS, that’s all I got to say.

So what can I say? It’s—you know, the money’s rolling in, and this is fun.

The problem isn't the comedians, it's the journalists who seek ratings rather than real news, and the people who only care about being entertained.