https://www.law.uchicago.edu/news/ginsburg-and-huq-how-defin...
The above is a "simple language" style definition. I am not a constitutional scholar but it seems a straightforward and useful one. There are many other such definitions on the 'net but most have similar elements.
To me we seem to have a clear fight among the executive and judicial branches, and the executive branch is doing everything in its power to ignore a Supreme Court ruling and the order of a lower court Federal judge.
For those who would argue that the US is NOT in constitutional crisis, I'm curious to hear your reasoning.