Meh. The lyin’ king won’t sign anything starting a war with a bunch of armed insurgents. They call them disgruntled immigrants or something like that in Paris. If they were really terrorists (can I use the “T” word?) no doubt he’d be “all in”. Meanwhile, back at D.C. comics world.
There is no provision for the President to sign or veto a declaration of war. It is not a bill subject to veto. It is entirely the prerogative of CONGRESS.
The president can only recommend that Congress declare war. He can't do it himself, nor can he veto a declaration of war.