US President Donald Trump arrived in the Netherlands on Tuesday to attend a NATO summit. He is expected to continue his calls for member countries to increase their defense spending.

Trump has repeatedly criticized European allies for relying on the US for defense, calling it unfair, and urging them to increase their defense spending to 5 percent of GDP.

In a government plane heading to the Netherlands, Trump took questions from reporters. He avoided giving a clear answer to a reporter asking if he is still committed to article five of NATO, which stipulates collective defense.

Under this principle, an attack on one member is an attack on all, and each member is expected to assist the party under attack by taking necessary actions, including a counterattack.

He replied: “Depends on your definition. There’s numerous definitions of article five.” He added that he is committed to maintaining friendships with many of the leaders.

Asked if he thinks he will meet with Ukrainian President Volodymyr Zelenskyy on the sidelines of the summit, Trump said, “Yeah, probably, I’ll see him. ” He added, “I’ll say ‘How you doing?'” and noted that Zelenskyy is “in a tough situation.”

This is Trump’s first Nato summit since starting his second term.