[VerySadAmerican]

That would be a true constitutional showdown. I don’t think the president can simply take over the NG unless it’s to deal with an emergency. I don’t believe he can take them over to NOT deal with an emergency.

[BuckeyeTexan]

I don’t think the president can simply take over the NG unless it’s to deal with an emergency. I don’t believe he can take them over to NOT deal with an emergency.

That's incorrect. Under Title 10 (U.S. Code), POTUS can nationalize the Texas National Guard in several ways and a state of emergency is not required in every case. Two examples are below. Note that each is exempt from Posse Comitatus.

• Use of Militia and Armed Forces to Enforce Federal Authority.
  Whenever the President considers that unlawful obstructions, assemblages, or rebellion make it impracticable to enforce the laws of the United States in any State or Territory, he may call into Federal service such of the militia of any State. This is another statutory exception to the PCA.
• Interference with State and Federal law.
  The President, by using the militia or the armed forces, or both, or by any other means, shall take such measures as he considers necessary to suppress, in a State, any insurrection, domestic violence, unlawful combination, or conspiracy.