Trump says U.S. is committed to mutual support of North Atlantic Treaty Organisation allies

"And this will lead very soon to an enhanced economic exchange, to better commerce, and this is what we all decide and what we wish, because we are responsible, President Trump and I, not only for the security, we are responsible for the well-being of our citizens, and this is what we are made a decision to do", Iohannis said.

Article 5 says an attack on one North Atlantic Treaty Organisation member is an attack on all members and binds the allies to come to that country's defense.

"It is not enough to speak to our NATO allies generally of "the commitments that bind us together as one" or note that 'we will never forsake the friends who stood by our side.' Each president since the treaty's signing has endorsed Article 5, and we call on you to do the same".

WASHINGTON (AP) - Punching back a day after his fired Federal Bureau of Investigation director's damaging testimony, President Donald Trump on Friday accused James Comey of lying to Congress and said he was "100 percent" willing to testify under oath about their conversations.

Portuguese Prime Minister Antonio Costa, NATO Secretary General Jens Stoltenberg, Greek Prime Minister Alexis Tsipras, U.S. President Donald Trump, Hungarian Prime Minister Voktor Orban and Britain's Prime Minister Theresa May pose for a family photo during a NATO summit at their new headquarters in Brussels, Belgium, May 25, 2017.

The only time that Article 5 was invoked was after the United States was attacked on September 11, 2001. The lawmakers warned of Article 5's importance to deter Russian aggression. It said that in addition to showing America's support of Poland, the trip will also emphasize the president's commitment to strengthening NATO's "collective defense".

A senior White House official later had said the United States does in fact support Article 5 simply by agreeing to the terms of the charter. "And you need to know you can also count on us!" But he said the USA would abide by its treaty obligations. "This is what we decided, President Trump and I, to make our partnership stronger, better, more enduring. Just by doing [that], he sent a strong signal".

"Do we ever go back and say, how about paying the money from many many years past?" said Trump.