The reason why Trump is going after these cities has nothing to do with the fact that they voted against him. Trump is going after these cities because they are not enforcing immigration laws that require them to collaborate with U.S. immigration authorities which lead to the reporting/detainment/deporting of illegal immigrants. If you enter this nation illegally, you broke the law and should be held accountable like anyone else who breaks the law. How would you feel if someone broke the law and then didn't get punished for it or were given a lesser punishment merely because of political correctness or interest by politicians?
I agree. Foreign matters (such as immigration and terrorism) should be left up to the federal government to decide. It's not to the states or to the cities. In an age of polarization, people would prefer if everything was taken at a federal level, but some things should be left up to the federal government as others are to cities and states.
The federal government should only handle issues like crime and punishment, Bill of Rights issues, foreign issues, and serious issues regarding civil rights, the environment and economics. Examples include the death penalty, protecting endangered animals, suppressing political correctness, and keeping same-sex marriage legal (and yes, it should be legal).
The state governments should take care of issues like moral issues (i.e. abortion), caring for citizens (i.e. Social Security), regulating controversial products (i.e. gun control), and important issues with the economy and environment.
If the law should decide on some things, but shouldn't be up to the state or federal government, it should go to the city government, such as city taxes, ordinances, and the lesser serious issues on the economy and environment (like recycling requirements).
Finally, other issues (like the bathroom debate, obesity, censorship, and behavior codes) should be left to the businesses and institutions, and not to the law. Those issues should stay out of politics.