What substantial government sanctioned monopoly does Comcast have? Can we point to something concrete rather than hand waving?

It's been illegal to grant monopoly franchises to cable companies since the mid 1990's. I don't know of a single market where Comcast is the only cable company because it has a sanctioned monopoly. There are a lot of places where Comcast has a de-facto monopoly because nobody else is willing to build high-speed service in a given area. But almost anywhere that's the case, it's because of telco-unfriendly regulations, not telco-friendly ones.

The people who rant about telcos can't get their story straight. They say Comcast has a legally protected monopoly, but then attack Verizon for not building fiber to the huge swath of places where the local governments are dying to get a competitor to the local telco. Their arguments are based on a false premise: that building fiber is profitable enough to justify the investment, and the government and telcos are getting in the way. The falsity of this premise is amply demonstrated when you look at places like New York, where the government has shoved the cable companies out of the way, but still has to drag Verizon kicking and screaming to build all this supposedly lucrative infrastructure.

On the other hand, Obama does not need to worry about his own re-election and it seems like quite a few Democrats threw him under the bus in the past election.