So how does this affect the US nation?
Too early to tell. For now, the only observable effect is that US oil production has increased for the first time in decades.
My personal opinion (warning, I'm not an expert in oil production or economics but I
am an "informed amateur" in economics) is that this whole fraking/shale oil thing is a scam (or a fad, if you prefer). Production costs are very high, the companies involved take on huge debts, and the output starts falling precipitously in just a couple of years. In the long run, it probably won't matter. The cheap oil is gone. We must either become more efficient or discover a new, more economical energy source.
for russia the falling oil prices wil have severe impact on the social security bills and deficits
Nor really, because of the falling rouble and also because Russia is starting to do more business with China and other Asian countries using currency swaps and avoiding the dollar altogether. It will have impact only on the Russian income from oil in US dollars and on Russian businesses who incur costs in US dollars. I don't have sufficient data to determine how significant those are but I rather doubt that they are as significant as you seem to think. Besides, Russia is perfectly capable of being self-sufficient. For now, Putin seems to be more concerned of the reaction of the hard-liners who accuse him of not taking more "decisive" steps toward Ukraine than of the reaction of those oligarchs who would be negatively affected by a falling oil price (when measured in US dollars).
We'll see.