If another country invaded the US Looking for something that was Non Existent, would he be held accountable?

For Example, if another President of another country said The US has this? Lets say Germany accused the United States of having a Laser powerful enough to wipe countries off the map. And Bush says, we don't have this laser, then the other president invades the US looking for the laser. After 8 years finds no laser , would that president be held accountable for being wrong? Like for example Saddam and Bush Switch places, and if Iraq had invaded the US looking for this Laser. Would Saddam just be able to walk away without consequences?