It means: On the one hand: if you are president and you authorize the nuclear bombings of Nagasaki and Hiroshima to get Japan to surrender without further loss

It means: On the one hand: if you are president and you authorize the nuclear bombings of Nagasaki and Hiroshima to get Japan to surrender without further loss of American life, you won't later be prosecuted for war crimes when your political rival comes into power. On the other hand, if you are president and you murder a Japanese person you see on the street when going for a stroll outside the white house, you can be prosecuted for that.