Trump said Newsom should be arrested. The California governor is initiating a lawsuit against the Trump administration. Their rivalry goes back years.

Gov. Gavin Newsom’s office, in a letter to the Trump administration, called the deployment of troops “unlawful” and a “serious breach of state sovereignty.”

The situation has all the elements that the president seeks: a showdown with a top political rival in a deep blue state over an issue core to his agenda.