"The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence."
-- US Constitution, Article IV, Section 4.
I'm no expert in legal-speak but I see this statement as follows:
The United States is required to protect the State of Washington (and all other states) if (let's say) Canada invades the state.
And, if the state legislature or the governor appeals to the federal government, then the United States is additionally required to act against domestic violence.
So, if the Governor wants Trumps to intervene, and makes a formal application, then it is a federal matter. But not before.