This looks like a setup for some dramatic political move, a kind of which WH wants full Senate backing on. Since WH has used other dramatic actions to convey its message short of direct immediate military action, this could be another way of declaring its serious intent, which also clears the way for potential full military action if everything else fails. Something along the line of defacto declaration of war.
If they are going to invite all Senators, it had better be good, not an anti-climatic photo op.