Russia would not hesitate to use tactical nuclear weapons

“Russia had privately warned Mattis that if there was a war in the Baltics, Russia would not hesitate to use tactical nuclear weapons against NATO.”

From Bob Woodward's new book, Fear: Trump in the White House.

 I assume they meant if Nato started such a war, in which case the Russian attitude is what one would expect - deterrence is why Russia and the other nuclear powers have the bomb. But how could Nato start a war IN the Baltic States which are members of Nato.

In any case, there will be no war in the Baltic States.