But he added: "In the end, that doesn't matter".
Already, the White House is saying that this is the beginning of a long-term process, not a one-shot, you know, we're going to get denuclearization right out of the gate and right away. And in just a little while, this historic first will take place in Singapore.
Washington is demanding the complete, verifiable and irreversible denuclearisation (CVID) of North Korea.
LIVE COVERAGE FROM ABC NEWSIn a meeting that seemed unthinkable just months ago, the leaders met at a Singapore island resort, shaking hands warmly in front of a row of alternating US and North Korean flags.
The agreement quickly broke down when the United States froze assets belonging to Macau-based Banco Delta Asia, which was suspected of laundering millions of dollars for the North Korean regime.
North Korea also wants security guarantees - a better relationship with the U.S.in order to end what it views as a hostile US policy.
The summit follows what had been a tumultuous 2017 for Trump and Kim, during which both men traded escalating insults and nuclear threats.
Should Trump agree to ease sanctions, Beijing is likely to be very willing to help North Korea rebuild its economy.
We can not afford to allow North Korea, despite sanctions, to continue the development of its missile program at unprecedented speeds in the way that Iran was permitted to do so.
In addition to discussing denuclearization with Kim, Trump has also left open the possibility of declaring an end to the Korean War.
"Yes, Donald Trump reached out", Rodman said, telling Cuomo he'd received a call from a person he described as Trump's secretary.More news: Deaths of African baobab trees linked to climate change
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He is scheduled to meet Kim for the first time at 9 a.m. North Korea was sharply concerned about security leading up to the summit.
In extraordinary scenes, Kim smiled as he walked and waved towards the crowd of tourists, families and media as a "woo" went up.
Although gaps remain over what denuclearisation would entail, Trump sounded a positive note in a lunch meeting with Singapore's Prime Minister Lee.
A sit-down with the U.S. president is something North Korea has long pushed for.
Kim says through an interpreter that it "was not easy to get here" and that there "were obstacles but we overcame them to be here".
Close US ally Japan has urged Trump to bring up the decades-old issue of its citizens abducted in 1970s and 1980s to train Pyongyang's spies in Japanese language and customs.
Some suggested that the fact that Kim was advertising the attractions of prosperity was a hopeful sign that he was serious about making security trade-offs to secure economic incentives. But he acknowledged the effort to rid North Korea of its nuclear arsenal was in its early stages.
Still, the road to the Singapore talks has been far from smooth.
So the summit was almost derailed by talk from Trump's hawkish National Security Advisor John Bolton of a "Libya model" of disarmament.
The Latest on the summit between North Korean leader Kim Jong Un and President Donald Trump in Singapore. Trump hasn't ruled out taking this kind of incremental approach; he said on Thursday that he didn't think it would be a "one-meeting deal".
"It's related to the North Korea-U.S. summit, so if anyone tries to go near the Yalu River, he or she will be accused of anti-regime crimes", the source said, referring to the waterway on the border between the North and China that is a popular route with defectors mainly when it freezes during the winter.