Constitution of the United States
Article IV
Section 4
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 TEXAS CONSTITUTION
ARTICLE 4. EXECUTIVE DEPARTMENT
Sec. 7. GOVERNOR AS COMMANDER-IN-CHIEF OF MILITARY FORCES. He shall be Commander-in-Chief of the military forces of the State, except when they are called into actual service of the United States. He shall have power to call forth the militia to execute the laws of the State, to suppress insurrections, and to repel invasions.