President Trump’s decision to engage directly with Kim Jong Un was premised on the bet that three decades of U.S. policy failures to contain North Korea’s nuclear program could be reversed by skipping over lower-level diplomatic talks and starting at the top of its authoritarian regime.

But 19 months after the two leaders’ first summit, the negotiations have broken down along the same sticking point as past efforts: how much sanctions relief the United States is willing to offer in exchange for how much of its arsenal Pyongyang is willing to dismantle.

Now, pressure is mounting on Trump to acknowledge that his strategy has failed and to change course, amid renewed warnings from Kim this week that the North would soon unveil a “new strategic weapon,” which analysts said could mean a long-range ballistic missile test. Diplomatic engagement has been dormant for months, and the Kim regime, frustrated by the stalemate, has publicly rejected Trump’s suggestion that the two leaders could soon meet for a fourth time.

“Regardless of your views about the wisdom of the original engagement between President Trump and Kim Jong Un, it’s taken place and it has produced virtually nothing,” said Evans Revere, a former Asia policy official at the State Department who left in 2007. “We now have a reaffirmation from the highest levels of the North Korean regime that they are determined to go as quickly as they can down the nuclear path. They are reiterating and strengthening some of their threats. This is essentially affirmation that nothing much has changed at the end of the day.”

For Trump, the growing tensions on the Korean Peninsula suggest that Kim is increasingly in the driver’s seat, as the president has sought to promote his North Korea strategy as a foreign policy triumph in an election year. Through a flurry of short-range ballistic missile tests in the second half of 2019, and in a lengthy speech on New Year’s Eve, the young dictator has made clear he has continued to prioritize the nation’s defense capabilities despite having announced a strategic shift toward economic development in 2018.

In recent weeks, Trump’s critics, including former national security adviser John Bolton and senators from both political parties, have faulted his approach and implored him to take additional steps, ranging from new economic sanctions to pursuing an interim deal with Kim.

So far, Trump has refused to alter his course, professing that his personal rapport with Kim remains positive and urging the North Korean leader not to violate that trust.

“I have a very good relationship with Kim Jong Un,” Trump told reporters Tuesday at his Mar-a-Lago golf resort in Florida. “I know he’s sending out certain messages about Christmas presents, and I hope his Christmas present is a beautiful vase as opposed to something else.”

But analysts said that even if Kim maintains a two-year moratorium on nuclear and ballistic missile testing, there appears to be a sense of diminishing returns in Pyongyang in dealing with a president saddled with the growing political liabilities of impeachment proceedings and a tough reelection slog.

“I think there are a number of reasons why engaging Trump at this point is probably viewed as a wasted effort,” said Suzanne DiMaggio, a foreign policy expert at the Carnegie Endowment for International Peace.

A White House spokesman declined to comment.

Warned in late 2016 during a White House meeting with then-President Barack Obama that North Korea would be his most serious foreign policy challenge, Trump quickly elevated the rogue nation’s nuclear program to the top of his foreign policy agenda. After ramping up economic sanctions and “fire and fury” rhetorical pressure in 2017, Trump jumped at an invitation from Kim to meet the following spring.

In explaining his decision, White House aides dismissed past nuclear talks, including the Agreed Framework in the Clinton administration and the six-party talks during the George W. Bush years, as having failed because of a lack of clear commitment from the uppermost ranks of the Kim family regime. Aides suggested that Kim, who had sent a delegation headed by his sister to the Winter Olympics in South Korea in February 2018, had signaled a strategic shift to diplomacy that made a leader-level summit a worthwhile gamble.

But in flipping diplomatic engagement on its head, Trump rushed into his first meeting with Kim in Singapore in June 2018 without the kind of detailed agreement that comes from painstaking working-level meetings, former U.S. national security officials said. After three days in Southeast Asia, Trump and Kim signed a half-page document consisting of four vague bullet points, including a pledge to “work toward complete denuclearization of the Korean Peninsula.”

Trump promoted it as a major breakthrough, pronouncing in a tweet that there was “no longer a threat” from the North.

But the president “misread entirely what it was they got out of Singapore,” a Democratic Senate foreign policy aide, who spoke on the condition of anonymity to discuss private conversations with administration officials, said Thursday. “It’s clear what North Korea thinks denuclearization constitutes and what it does not constitute.”

Analysts have said North Korea has long defined the term as meaning the United States would withdraw its nuclear-defense umbrella from South Korea and Japan as a prerequisite for any large-scale dismantlement of its own program. The gap between the sides became clear as diplomatic teams failed to hammer down a clear definition of “denuclearization” in the wake of the Singapore summit.

Despite a lack of progress, the two leaders agreed to meet again, in Hanoi last February. But a working-level meeting ahead of the summit failed to make advances on a road map for a denuclearization process. Talks broke off in Hanoi after Trump demanded Pyongyang relinquish its entire nuclear program in exchange for broad sanctions relief, while Kim countered with a more incremental plan.

Analysts said Trump failed to bestow authority in his negotiating team to speak for him in the same manner that his aides suggested the Kim family had long failed to do with North Korea’s negotiators, leaving aides unable to translate the good feeling from Singapore into tangible, detailed agreements.

“The North Koreans were convinced the only person they could really deal with was Trump,” said Christopher R. Hill, who served as the Bush administration’s lead negotiator during the six-party talks with North Korea.

Efforts to restart talks since Hanoi have been fruitless, despite Trump becoming the first sitting U.S. president to set foot in North Korea during a brief handshake meeting with Kim at the Korean demilitarized zone in June.

Many lawmakers on Capitol Hill and foreign policy analysts said the United States is in a worse position now than two years ago, as North Korea has continued to develop its nuclear program while the Trump administration has halted some joint military exercises with South Korea and the international sanctions regime assembled in 2017 has been weakened.

Brookings Institution analyst Jung Pak, a former U.S. intelligence official on Korea issues, said the outcome has convinced her that the North Korean leadership was never serious about a policy shift away from nuclear development even as it embraced Trump.

“The question looking back is: Were we in a special moment in 2018 and 2019? I don’t think it was. It was a blip rather than a big inflection point,” Pak said. “The U.S. and North Korea are fundamentally at odds in their strategic objectives. No amount of letters or phone conversations or summits at the leader level is going to shake that loose.”