He goddamn can now. They still don't have the shooter in custody. Not finding this guy is the worst case scenario. If the shooter could be anywhere, Trump has an excuse to crack down everywhere. We are going to have to live with this.
Of course we're going to have to live with this, just as we're going to have to live with everything else the regime has done and will do.
However (and this was my sarcastic point), the pattern up until now is to send the guard into democratic strongholds using crime as an excuse. He was gung-ho about sending them into Chicago, but the GOP has started to back off that one, probably in response (in part) to Illinois Gov. J.B. Pritzker's strong rhetoric against it, the horrible morale of the troops sent to D.C., and the wholly negative public opinion polls in regard to the Guard being used this way.
Those of us with working brains who care about reality know that crime rates have been dropping for years, and that the per-capita crime rates are higher in red states overall. So why hasn't he sent them to, say, New Orleans, Memphis, or St. Louis? Because that doesn't fit the narrative of Blue states being lawless wastelands, not to mention the need for some form of support from Red State governors.
So, could he deploy the Guard to Utah? Yes. Will he? I'm not so sure about that. Regardless, time will tell just as it always does.