Subconsciously, we human beings, as creatures of cognitive psychology, often associate the concept of law with the concept of ethics. However, as someone who has taught ethics courses at three state universities, let me share one of the basic points of Ethics 101, namely, that law and ethics are very different entities.
Laws are not necessarily, or even likely to be, ethical. Conversely, ethical ways of behaving can be outright illegal.
When "law" backs the ascent of a fascist like Donald Trump, when "order" means thuggish, racist, and even murderous police enforcement, then law & order become the opposite of morality, justice and their deep association with the founding ethical principles of this country.
These principles include "self-evident" truths. They include equality, equal justice under law, the right to freedom of speech and freedom of assembly.
Again, law and order are not automatically good. Look at North Korea. Look at China. Plenty of law & order. And yet also evil. Atrocity. Brutality. Mind-control. Surveillance. Oppression of all basic freedoms.
Democrats would be wise to counter Trump's framing with a simple, clear point: "law & order," as used in his rants, is the opposite of Truth, Morality and Justice. In association with the latter, our Founders insisted on a Bill of Rights and a Declaration of Independence.
Trump's "I am the LAW & ORDER President" is a dictator's proclamation. He perverts law and order, makes it dirty, as he does with so much else.