McCain book: US should consider cyberattack to punish Putin

I thought a cyberattack was an act of war? If that is true...then why not nuke Russia, better to do it before they do it to us..... but the reality is to openly say you are going to do an act of war is not good. Also, if this is to punish Putin, why no mention of the President who did not protect us? No one complains about Obama not protecting us during this election. I heard all the Problems of this election were Trump, but he was not POTUS? Makes no sense to me.