The National Guard, it is hoped, will impose some kind of order on the situation through a combination of superior discipline and overwhelming force. In practice this will probably involve implementing some kind of domesticated COIN strategy involving carefully executed information operations and expanding perimeters of control.
The aim of the former will be to justify the latter. Expect a lot of extremely visible public diplomacy - press conferences, staged peace rallies, town hall meetings - as well as police-supplied footage of various crimes. All disseminated to advance a distinction between "good" protesters who want peace and dialogue and who are worthy of civil rights, and "bad" protesters who just want anarchy and violence, and who are not only unworthy of civil rights but, crucially, who are ruining things for everyone else. Draconian measures like curfews will be spun as unfortunate but necessary measures police have been forced to impose for the protection of the "good" Fergusonites.
This is more or less what has already been happening, but the Ferguson police have proven themselves terrible at it. The new boots on the ground may have slightly better training, though they'll also enter Ferguson as an alien force with even fewer community ties than the crackers who've screwed things up so far. But the real difference maker will be the new regime of command-and-control and their superior media resources. It is only a matter of time before the national news gets bored with covering this story with any rigor and becomes hopelessly ensnared in the narrative the authorities will lay out for them, with maybe the occasional sordid and scandalous expose for ratings when they can find some good material.
If any of this seems familiar, it's because some variation on this happens every single time. Capitalism usually relies on pacifying and atomizing the population in order to maintain order, but faced with actual resistance it must rely, in the final analysis, on the overwhelming brute force of the police state. That's the context in which calls for demilitarization by the Rand Paul right need to be understood. He is not calling for a less militarized society, but simply a less militarized state - one which has abdicated its police powers and turned them over to the private sector.
The left, of course, is calling for something different: for a society with less militarization, period.
But that means a different society altogether. And that means even more conflict than what we have seen in Ferguson, not less. You can see the introduction of the National Guard as the first step in a return to the oppressive but superficially peaceful status quo, or you can see it as the unfortunate end of a nascent revolution that should get a lot more violent and destructive before all is said and done. But it is crazy to imagine that we can fix these problems without violence, as if Capital was ever not going to call in the National Guard when things got bad enough.