Tensions between the U.S. and its NATO allies have cooled off since most of the alliance's member states agreed to increase their defense spending from 2 percent of GDP to 5 percent by 2035, which many Trump supporters say is proof that his hard-charging negotiating tactics, even among friends, produces results.

The vice president, long a skeptic of US military intervention, is the rare figure in the administration who can appeal to both the realist and hawkish wings of the GOP.