SCOTT SIMON, HOST:
Fifty-five wooden boxes wrapped in blue-and-white U.N. flags arrived in South Korea yesterday. They were on a U.S. military flight from North Korea. The boxes possibly hold remains of some of the more than 5,000 U.S. GIs who went missing in Korean War battles more than 65 years ago. At the White House, President Trump had only praise for Kim Jong Un.
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PRESIDENT DONALD TRUMP: I want to thank Chairman Kim in front of the media for fulfilling a promise that he made to me. And I'm sure that he will continue to fulfill that promise.
SIMON: Now, returning the remains of U.S. troops was indeed a promise Kim made to Trump last month in Singapore. But as NPR's David Welna reports, doubts remain about the bigger commitments like denuclearizing the Korean peninsula.
DAVID WELNA, BYLINE: Just hours after the boxes of what are hoped to be American soldiers remains landed in South Korea, Defense Secretary Jim Mattis was asked by a reporter at the Pentagon if this gave him more confidence that North Korea would also follow through on its promise to denuclearize. His response was upbeat.
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JIM MATTIS: I think when you have that sort of communication going on, it sets a positive environment, a positive tone for other things, more important things in terms of international diplomacy. But this humanitarian act obviously is a step in the right direction.
WELNA: But maybe the only step. The American who commands all U.S. and U.N. forces in South Korea detects little progress. Army General Vincent Brooks said last week that when it comes to North Korea's nuclear weapons program, it's business as usual.
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VINCENT BROOKS: The systems and capabilities that they have are not gone. So all of the capability, really, that was there before is still in place and still intact. What is the intention that goes with it?
WELNA: That's what the Senate Foreign Relations Committee wanted to know as well when Secretary of State Mike Pompeo appeared before it this week. Bob Menendez, the panel's top Democrat, pointed out that it's been nearly two months since the Singapore summit.
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BOB MENENDEZ: In that time, we have yet to hear or see anything that provides us with real confidence that North Korea, as the president gloated, quote, "no longer poses a threat."
WELNA: Pompeo remained optimistic.
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MIKE POMPEO: Nothing's changed. Our objective remains the final, fully verified denuclearization North Korea has agreed to by Chairman Kim Jong Un.
WELNA: Colorado Republican Cory Gardner wanted to get more specific.
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CORY GARDNER: When will we know if North Korea is moving toward denuclearization - concrete verifiable steps?
POMPEO: I don't know. I don't know the answer to that.
WELNA: And Massachusetts Democrat Ed Markey scoffed at reports that North Korea was dismantling a missile test site, calling that an empty gesture. He then posed a pointed question.
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ED MARKEY: North Korea continues to produce fissile material, nuclear bomb material. Is that correct?
WELNA: After briefly hesitating, Pompeo confirmed this was true.
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POMPEO: Yes. They continue to produce fissile material.
WELNA: And that lead Markey to this conclusion.
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MARKEY: I am afraid that at this point, the United States, the Trump administration, is being taken for a ride.
POMPEO: Fear not, Senator. Fear not.
WELNA: Pompeo said he hoped North Korea would denuclearize before Trump's first term in office is over.
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POMPEO: We're engaged in patient diplomacy. But we will not let this drag out to no end.
ANDREI LANKOV: The North Koreans' goal is quite clear. They want to out-wait Donald Trump administration.
WELNA: That's Andrei Lankov, a Russian-born expert on North Korea who was recently there. Under no circumstances, he says, would North Korea's leaders agree to surrender their nuclear weapons.
LANKOV: However, they are willing to make concessions. They are going to slice salami in very thin pieces and give something to the American side. But they want everything to be as thin and small as possible. And they want to give it as infrequently as possible.
WELNA: Starting, perhaps, with those flag-wrapped boxes. David Welna, NPR News, Washington. Transcript provided by NPR, Copyright NPR.