If this happens, it will be the official start of WW3.
By the way, this was predicted by a high-ranking American military officer, months ago. He put it in these terms:
We are not sure where Putin will attack, but we are sure he will use the interim to the Presidential Elections in the United States for gaining more territory through a surprise attack, namely when the public in the United States is wary of war and focused upon the outcome of the elections. This will then put the new American President in front of a fait accompli.
(Quoted from Memory)