Please explain how enforcing Article 4 Section 4 is a bad idea. Are you some kind of troll?
It doesn't apply to this situation. The reason the guarantee of state government and defense of invasion come one after the other there springs from the concern that a foreign military or other organized armed force might invade a state and stage a coup or establish a dictatorship. That isn't whats happening. A poorly managed immigration policy isn't an invasion, it's poor execution of policy. Using the military to enforce public policy is a violation of Posse Comitatus.
It seems to me that President Trump is doing a pretty good job of improving the border though the wall could be coming along a bit faster.