No it isn't. Only a direct attack by our forces would be a belligerent act. As I said, we are only co-belligerents. Which also means any purported Constitutional restrictions do not apply.
You can make the argument that doing so is risky, might provoke the Russians to escalate, etc., which are rational if not (as I believe) valid arguments. But you can't invent new law out of whole cloth to get your preferred policy choices. That's what the Left does.