Those concerns, according to a senior White House official, began about two weeks ago when a North Korean delegation failed to show up at a planning meeting for the summit with U.S. officials – although, according to the official, the U.S. will be sending a delegation back to Singapore later this week for yet another sit-down.
"Our eyes are wide open to the lessons of history, but we're optimistic that we can achieve an outcome that will be great for the world," Pompeo said. "Our posture will not change until we see credible steps taken toward the complete, verifiable, and irreversible denuclearization of the Korean peninsula."
Pompeo's remarks came just a day after President Trump seemed to open the door to incremental concessions to North Korea in the event it started taking steps to denuclearize, appearing to back away from a demand that it happen immediately and completely.
"It would certainly be better if it were all in one. Does it have to be? I don’t think I want to totally commit myself," Trump said before his meeting with South Korean President Moon Jae-in.
But Pompeo seemed to contradict that Wednesday, telling Congress, "We're not going to provide economic relief until such time as we have an irreversible set of actions – not words, not commitments – undertaken by the North Korean regime." He denied there was any daylight between Trump and his National Security Adviser John Bolton on the issue.
On Tuesday, Trump also tempered expectations for the summit happening on its previously announced date, even as the White House and State Department said it continues to move forward as if it's on schedule.
"So there's a very substantial chance that it won't work out, and that's okay," Trump said alongside Moon in the Oval Office. "That doesn’t mean it won't work out over a period of time. But it may not work out for June 12th."
Speaking to reporters on the South Lawn Wednesday, President Trump said he expects a final decision on if the June 12 date will be locked down by next week, after the U.S. delegation returns from its meetings in Singapore.
Trump on Tuesday also laid out some specifics on what the U.S. would be willing to offer in exchange for positive results in the negotiations, including protection from any potential attempts at regime change to overthrow Kim and a surge of economic benefits for the country.
"We will guarantee his safety," Trump said. "And we've talked about that from the beginning. He will be safe. He will be happy. His country will be rich."
Pompeo declined to offer specifics, but said the U.S. was "prepared to do the things that provide him the comfort and security" that the regime has been seeking through nuclear weapons.
The U.S.'s top diplomat – who is also the highest-ranking official to have met Kim – also repeated that the U.S. was offering economic assistance, a prospect he said Kim understood: "He has shared candidly that he understands that economic growth for his people depends on a strategic shift [from nuclear weapons], and we hope he's prepared to make that," he said.
But last week, North Korea's first vice minister of foreign affairs Kim Kye Gwan rejected U.S. economic support, saying in a statement, "We have never had any expectation of U.S. support in carrying out our economic construction and will not at all make such a deal in future, too.
In fact, in the face of the various diplomatic carrots floated to encourage the North Koreans, it remains unclear whether there's been a change of posture since senior officials in the country last week publicly scolded South Korea and the U.S. over a pre-planned joint military drill and rhetoric from Bolton.
"It is ridiculous comedy to see the Trump administration, claiming to take a different road from the previous administration, still clings to the outdated policy on the DPRK," Kim Kye-gwan's statement also said.
At Wednesday's hearing, Pompeo still expressed hope that the North Korean position mirrored the personal assurances he said he received in his two meetings face to face with Kim Jong Un.
"There's places where we still have lots of work to do to find common ground," he said, but added later, "I'm convinced that we have both the timing and in this case the leaders right for this meeting to have an opportunity to be historically successful."
Amid criticism of the administration for working with a brutal dictator with a terrible human rights record, Pompeo said the issue "was raised directly between me and Chairman Kim" and will be part of Trump and Kim's discussions. He declined to say whether it'd be part of any final deal, however, because at this point there are only "broad outlines of what each nation is prepared to do."