The framers only left it to the Governor's in extremis, because in the case of invasion there may not be time or opportunity to convene the Legislature.
"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.
Frankly, I think the chances of a Legislature doing this are higher than getting a Governor to stick his neck out so far.
"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.
The 'and' indicates that such is another element of a list; therefore the guarantee of protection [in case of invasion] is separate from that of the "application of the legislature*".
Or would you say that this would prevent Amendments 9 & 10 from allowing, say, New Mexico's constitution to say the following?
Art V, Sec. 4. [Governor’s executive power; commander of militia.]
The supreme executive power of the state shall be vested in the governor, who shall take care that the laws be faithfully executed. He shall be commander in chief of the military forces of the state, except when they are called into the service of the United States. He shall have power to call out the militia to preserve the public peace, execute the laws, suppress insurrection and repel invasion.
* or executive [when...]
Hm, you think so? Why?
(Forgot to ask this when replying.)