Kim Jong-un’s commitment to America’s goal of dismantling North Korea’s decades-old nuclear program remains uncertain amid the looming denuclearization summit between the dictator and U.S. President Donald Trump, experts told lawmakers on Tuesday, echoing some regime defectors.

The expert’s testimony before a Senate foreign relations subcommittee came as the U.S. and North Korea are preparing for a potentially historic summit in Singapore on June 12 during which Trump is expected to demand that Kim take steps towards complete, verifiable, and irreversible denuclearization in exchange for sanctions relief.

Asked whether Kim is committed to dismantling North Korea’s nuclear program, Dr. Victor Cha, a North Korea expert at the Center for Strategic and International Studies (CSIS), responded in the negative, adding, “I’m quite skeptical.”

Cha, who is also a fellow in human freedom at the George W. Bush Institute and a professor at Georgetown University, explained:

In my 30 years of studying this issue and the limited time I’ve had in government working on this issue, I am not convinced yet that … he is fully ready to give up his weapons. … [North Korea prefers] to front-load our rewards and push off denuclearization for as long as they possibly can.

…

I’m quite skeptical that he is [committed to dismantling North Kore’s nuke program] and let me just give you one reason why … over 50 years [since 1962] they’ve been working on this thing [one nuclear site alone] and the notion that they’re ready to show up in Singapore and all of the sudden say here it’s all yours now, we’re ready to denuclearize. I’m just very skeptical of that.

Citing his studies late last month, human rights activist Kim Young-hwan, a former supporter of North Korea, told reporters that it is “impossible to find the whereabouts of all nuclear weapons in North Korea.”

During the Senate panel hearing, witness Joseph Yun, a North Korea expert at the United States Institute of Peace (USIP), also indicated that uncertainty surrounds Kim’s commitment to denuclearization, noting that if history is any guide, North Korea will not dismantle its nuclear program.

Nevertheless, Yun and Cha agreed that the possibility of Kim being “serious” about breaking up North Korea’s nuclear plan is a “hypothesis” worth examining at the planned summit.

Yun told Senators:

We don’t know [if Kim is committed to denuclearization] and I think this is a hypothesis worth testing….let them [Trump and Kim] have a go. We can say it failed many times in the past, but we’ve never had the leaders meeting on this issue

Consistent with the experts’ testimony, Thae Yong-ho, a North Korean government defector, warned in a press conference on May 14 that Kim “will never give” his nuclear program up.

On Tuesday, both experts told lawmakers that Kim would likely insist on maintaining a civilian nuclear program for peaceful purposes, arguing that other countries can do so.