Updated: 10:38 a.m. ET
President Trump meets at the White House Wednesday with the secretary general of NATO, Jens Stoltenberg.
Afterward, the two men will take questions from reporters, which are likely to center on the administration's commitment to the North Atlantic alliance as well as last week's deadly chemical weapons attack in Syria.
White House officials say the president will reaffirm the U.S. commitment to NATO and its "ironclad" pledge to defend NATO allies, even though Trump repeatedly questioned the relevance of the alliance during the campaign. He's also complained about countries that don't spend enough on their own defense, and suggested the U.S. would review those payments before deciding whether to come to an ally's aid.
Secretary of State Rex Tillerson raised the issue of defense spending late last month at a NATO meeting in Brussels.
"As President Trump has made clear," Tillerson said, "it is no longer sustainable for the U.S. to maintain a disproportionate share of NATO's defense expenditures."
Each NATO country has pledged to spend 2 percent of its gross domestic product on its own defense by 2024. Only a handful of alliance members meet that target now. U.S. defense spending accounts for somewhat over 3 percent of its GDP. Germany spends only about 1.2 percent of its GDP on its defense.
After a meeting with German Chancellor Angela Merkel in March, Trump complained that "Germany owes vast sums of money to NATO & the United States must be paid more for the powerful, and very expensive, defense it provides to Germany!"
NATO's secretary general says defense spending is only part of the picture, though.
"We need many different tools to stabilize our neighborhood," Jens Stoltenberg said last month. "It's not either development or security. It's development and security."
Trump's proposed budget for the coming fiscal year would boost U.S. military spending by 10 percent, while making deep cuts in development and foreign aid.
Likewise, Trump wants to cut by half the number of refugees the U.S. takes in. He's criticized Merkel for Germany's welcoming attitude towards refugees.
For all his questions about NATO, Trump looks forward to adding a new member to the alliance. The tiny Balkan nation of Montenegro has been approved to join NATO and is expected to take part in an alliance meeting next month.
White House officials note that Montenegro already spends relatively more on its own defense than most other NATO countries — 1.7 percent of its GDP.
Russia is strongly opposed to any Western tilt by Montenegro and its Balkan neighbors. White House officials say they're concerned by possible Russian meddling in Montenegro's election last October.
Trump had previously pushed for improved ties with Russian President Vladimir Putin, but Trump has been cooler towards Moscow since last week's chemical weapons attack carried out by Russia's longtime ally, Syria.
"Putin is backing a person that's truly an evil person," the president said this week in an interview with the Fox Business Network. "I think it's very bad for Russia. I think it's very bad for mankind."
Aides say Russia's conduct has only "reinforced" Trump's commitment to working with NATO.