They can and will—some already are. And more importantly they need to do it together. It will therefore be through the US Conference of Mayors, through our new Global Parliament of Mayors, through organizations like the C40 Cities that work on climate change. One by one, they’re not very strong. But when cities act together and pool their resources, their populations, their majorities, they become very strong indeed.
People have come to expect a certain amount of protection and actual civil liberties in their cities and states. Even though Trump won the election, he doesn't have the right to actually rule. Governing needs to be done within the framework of the checks and balances which exist in the US. There are areas where states have some autonomy, and there are moral codes which government officials, mayors, and governors should uphold even against the wishes of someone such as Trump.
All people who believe that Donald Trump should not be running our country should be standing up against him. Nobody should be turning their backs, especially when they see what kind of mess Trump is going to cause. Who cares about public opinion? Of course certain people are going to be upset, but most of these people don't care enough about others to deserve a thought.
Yes, more mayors should stand up against Trump like DiBlasio did. What better time is there for our leaders to stand up and defend those they represent. Our presidency, our government, and the fundamental beliefs that our country is based on are all at risk right now. If not now, then when should they stand up?