I’m not sure how the militia is supposed to be organized, I know its has be under State law, but under several different statues it is considered a separate entity from the Texas State Guard which is itself a separate entity from the Texas National Guard. Which is important because Bush put all the National Guard units under the command of the President, removing the Governors as the ultimate authority.
The President has been able to call up the National Guard since before WW-II. The feds pay (most of) the bills so they call the tune. They were so called for WW1, WW2, Korea, selectively for Vietnam, Desert Shield/Storm, Enduring Freedom and Iraqi Freedom.
It wasn't Bush, he merely exercised his authority to call them up. An Authority which derives from Art I sec 8 of the Constitution, which gives Congress the power..
To provide for organizing, arming, and disciplining, the Militia, and for governing such Part of them as may be employed in the Service of the United States, reserving to the States respectively, the Appointment of the Officers, and the Authority of training the Militia according to the discipline prescribed by Congress;
Historically the states neglected their militias, failing to keep them trained, and equipped. Congress also failed to provide appropriate organization, discipline (meaning standard training, standard calibers, etc) and most importantly for arming them.
State Guards, which several states have, cannot by law be called involuntarily into federal service. They can be "loaned" to other states, via bilateral agreements, and have been for natural disasters and such. State Guards may not however train with arms, per laws passed by Congress.