What evidence are you basing this claim on? Or is this pure speculation? I know Trump made the claim, but he's made a lot of claims that have yet to be substantiated. What is your reasoning for thinking this statement was about partisan politics and not frustration with the DHS secretary? It just seems far more likely that the mayor was upset at the DHS Secretary for saying it was a "good news story" when people are still dying.
Do you have any sources that aren't the Daily Caller that make this claim? It is a very well known right biased, sometimes dishonest, super conservative website that is considered nearly "extreme right" by media/bias fact check (
Daily Caller - Media Bias/Fact Check). I'm not saying it's untrue, I just don't trust outlets on either side that are regularly so biased. Just so you know, I feel the same way about Slate and Salon Magazine.