NATO must "expect the unexpected" and prepare for a Russian attack, Dutch Admiral Rob Bauer, the alliance's military committee chief, said in Brussels last January. Meanwhile, intelligence and military officials have warned in recent weeks that NATO member states must be ready for a potential conflict with Russia.

This week’s breakthrough on an economic cooperation deal with Ukraine is unlikely to soften Russian President Vladimir Putin’s resistance to President Donald Trump’s peace plan — and the White House isn’t sure yet how to change that.