Alternatively: a president declaring war should first kill a randomly-selected soldier with their own bare hands, livestreamed on television. It would make war real to them, and not just some non-people disappearing into a bomb explosion on a video screen.
Something similar has been suggested for starting nuclear war: if things are bad enough that you are willing to doom whole populations of mostly-innocents to their death, you shouldn't have any trouble directly killing one more.
You could make it even more symbolic by doing it as seppuku instead: if you have failed badly enough as a politician that politics isn't even an option anymore and many soldiers have to pay the ultimate price to make up for your failure, then you should be the first one to do so.
Something similar has been suggested for starting nuclear war: if things are bad enough that you are willing to doom whole populations of mostly-innocents to their death, you shouldn't have any trouble directly killing one more.
You could make it even more symbolic by doing it as seppuku instead: if you have failed badly enough as a politician that politics isn't even an option anymore and many soldiers have to pay the ultimate price to make up for your failure, then you should be the first one to do so.