For 30 Rock and Parks and Rec, weren't those appearances after the people were already prominent and/or in office?

The 30 Rock/Al Gore example in particular happened years after he was done running for public office.

And even Parks and Rec wasn't so much advocating for Joe Biden/Michelle Obama as having a left leaning, political character be excited about the opportunity to meet them. I can also remember John McCain appearing on Parks and Rec.

On that note, recall that NBC's SNL had Donald Trump HOST the show in late 2015, during the campaign. How nuts does that seem now, given how much the writers hate him?

I think the fall from grace narrative arc was very entertaining. Most political candidates get to do hits on Late Night shows in a relaxed atmosphere whenever they want. I think it's a great part about America.

30 Rock also pushed Obama a bit if I recall correctly and before the election - but they also cracked a joke about how Tina Fey's character would tell everyone she was voting for Obama but then secretly vote Republican.

So think what you will of that.

Newt Gingrich too on Parks and Rec.

A writer pushing their political agenda is one thing and something you can't quantify. Is there a department at ABC whose sole job is getting politicians to pay for guest appearances?

This is key. It's one thing to have creative staff that lean left, it's another for the injection of political propaganda to be the product itself. In that case, there's incentive for ever increasing amounts of propaganda (until it becomes so omnipresent that there's no marginal benefit to the buyer to having more of it, which would be pretty dystopian).

Hey now, 30 Rock had Condoleeza Rice!

I hate to ruin your thesis, but:

Parks and Rec also featured Newt Gingrich, Olympia Snow, and John McCain.

What thesis is that?