I think it's Putin reiterating his stance on the expansion of NATO. He's so against it because it would be closer to his borders.
What is your opinion of the Russian fighter jets flying over the U.S. destroyer..... flying 30 feet away, with multiple passes?
It's a harbinger.
The US and Russia have a history of provoking each other (exercises in the Baltic are legitimate but about as diplomatic as a Russian nuclear vessel conducting exercises of Los Angeles). The flyover is typical Putin (compare his tactics in Syria where he claims one thing but does another) and, as such, show him to be of the same ilk as Kim Jong-Un.
Why is it a harbinger? Because if Americans are foolish enough to put a blustering jac kass like Trump into the White House, he will lack the wisdom and the restraint to handle this kind of situation. If such happens we could be looking at global catastrophe.
They've done it before so it's nothing new but Putin is a megalomaniac and is trying to prove to the world that he wants the old Soviet East Bloc countries back under his rule. Trying to scare us and N.A.T.O. Away. Foolish mistake on his part.