"The United States has demonstrated not merely with words, but with it actions, that we stand firmly behind Article Five," the president said, referring to the mutual defense commitment.
But he said that more defense spending was needed on the eastern side of the Atlantic, "for its own protection, and you know this. Everybody knows this. Everybody has to know this. Europe must do more."
Article 5 is the North Atlantic Treaty's key provision. Under Article 5, an attack on any NATO member is considered an attack on all.
President Trump is meeting the heads of state of the Three Seas Initiative, which encompasses 12 countries from the Mediterranean and the Black Sea to the Baltic Sea belong, including Latvia's President Raimonds Vejonis.