RACHEL MARTIN, HOST:

This is WEEKEND EDITION from NPR News. I'm Rachel Martin. President Obama leaves tonight for the Netherlands. It's the start of a four-nation trip that includes a meeting with the pope and a visit to Saudi Arabia. But the crisis in Ukraine will hang over his agenda. NPR's Ari Shapiro will be on the trip. He joins us now. Hi, Ari.

ARI SHAPIRO, BYLINE: Hi, Rachel.

MARTIN: Give us a sense of what we expect to happen tomorrow when the president and other world leaders meet at The Hague.

SHAPIRO: Well, this is a nuclear summit that has been planned for years. One of President Obama's top national security initiatives from the time he took office was keeping nuclear materials out of the hands of terrorists. That's what this summit is about. One of the key partners with the U.S. in this nuclear disarmament project has been Russia, and, of course, the situation in Ukraine now overshadows all of that. There are real questions about whether Russia will continue to cooperate with the nuclear disarmament project, and also questions about how much the nuclear summit will be able to keep to its agenda when Ukraine is, to some extent, is sucking all of the air out of the room.

MARTIN: So, the shadow of the Ukrainian crisis looms large, but are there specific formal talks about the Ukraine scheduled for the president?

SHAPIRO: Yes. The president has called a meeting of the G7 - that's the group of seven industrialized nations. We often talk about the G8. The eighth is Russia, which is, needless to say, not part of this meeting that will take place on the sidelines focused entirely on Ukraine. So, you have this kind of split-screen situation where world leaders are trying to work together with Russia on nuclear disarmament, while at the same time sort of aligning against Russia on the issue of Ukraine, sanctions and so on.

MARTIN: From The Hague, President Obama flies on to Brussels in Belgium. What's going to happen there?

SHAPIRO: Well, originally, the focus of that visit was going to be trade talks between the U.S. and Europe. Now, it seems that, again, Ukraine will dominate the conversation. President Obama is going to visit NATO headquarters. NATO has taken on a big role in this situation. And it's in the same city where the EU had its spring meeting, where European Union officials decided to put new sanctions in against Russia, signed a new agreement aligning Europe with Ukraine. And so the outlook for Brussels has really changed as well.

MARTIN: What does that mean for NATO? You say their organization is now taking on a bigger role in the Ukrainian crisis. This is, obviously, the North Atlantic Treaty Organization. This is a defense alliance that was for many years established as a counterweight to the Soviet Union.

SHAPIRO: Yeah, and it's interesting timing because for the last decade or so, NATO's main focus has been Afghanistan. And, of course, this year ends the combat mission in Afghanistan. And there's been this real question about what is NATO's role going into the future. Well, to some extent, that question has been answered. There is now a global crisis right in NATO's backyard and it is becoming the new focus of this military alliance.

MARTIN: NPR's Ari Shapiro, speaking with us from our London bureau. Thanks so much, Ari.

SHAPIRO: You're welcome. Transcript provided by NPR, Copyright NPR.