[Targan]

With Tokugawa being an existing major player in the Vegas scene, he must have had solid links to some pretty serious underworld figures. Maybe he had some dodgy side businesses going on pre-war (illicit substances, firearms, human trafficking perhaps related to the sex industry). If, in the lead up to the TDM, he was able to play some of those forces off against one another with an eye to consolidating them under his own banner, that would give him an excellent pool of muscle to draw on once the fertilizer hit the ventilation.

Alternatively or in addition, perhaps he had a major financial stake in labor hire and/or private security companies. Both of those areas would provide excellent synergies with his casino interests.