Should we react the same way to a cyber attack on national infrastructure as we would if there were a 'traditional' physical attack?

This is an interesting question. US reaction to 'traditional' physical attacks are many times not supported in real proof about the origin or even the reality of such attacks. A recent example being the chemical attack attributed to Assad, which Trump responded by bombing a Syrian Arab Army air base, killing a number of soldiers.

History tells us very clearly that when the US wants to attack some nation, generally in the Third World, it will basically use any excuse at hand, your perspective suggest a new kind of excuse, perhaps even easier to use, due to its nature and how hard it is to discover its origin without a doubt.

The Russian 'hacking' affair is months old and as you wrote: "they likely hacked a democratic process"... still not a sure thing. If they accuse any country of hacking with (sometimes anonymous) intelligence claims that show no proof, who will stop them, the press?