The vague, one-page document Trump and Kim Jong-un signed does not commit the United States to lifting sanctions on North Korea, but North Korean state media claims Trump told Kim that he will lift sanctions.
From Bloomberg:
The report from the Korean Central News Agency, which was published after Kim returned home from his meeting, noted Trump’s vow to suspend U.S. military drills in South Korea. It also said Trump committed to unspecified “security guarantees” for Pyongyang, and to “lift sanctions against it.” [...]
Trump said sanctions would stay, at least until the isolated nation moved to give up its nuclear arsenal. But there have been slight differences in recent comments among senior U.S. officials as to whether that means North Korea must first complete denuclearization -- and have it verified -- or if some goodwill steps would be enough.
Now, this is North Korean state media so we can't be certain if what they say is true, but this certainly rings true, doesn't it?
The fact is we don't know know what Trump and Kim said to each other during a short period of time when they were only accompanied by their translators. And, for his part, Trump has a documented habit of blurting things out (including classified information) when he meets face-to-face with dictators he admires.
Moreover, Trump tweeted this morning that North Korea is "no longer a nuclear threat" even though Kim Jong-un hasn't given up anything.
Just landed - a long trip, but everybody can now feel much safer than the day I took office. There is no longer a Nuclear Threat from North Korea. Meeting with Kim Jong Un was an interesting and very positive experience. North Korea has great potential for the future!
— Donald J. Trump (@realDonaldTrump) June 13, 2018
With Trump declaring that North Korea is no longer a threat, it's only a matter of time before he calls for lifting economic sanctions and possibly even withdrawing American forces from South Korea.
And Kim Jong-un will keep his nukes.
There is another threat here and that's the possibility that Trump will eventually realize he's getting nothing and will attempt to reassert dominance over North Korea with another threat of "fire and fury." Who knows what Trump will do if he suddenly feels like he's been humiliated in front of the entire world?
What North Korean state media is telling their citizens is significant in itself, even if Trump didn't pledge to lift sanctions, because there was no mention of giving up their nuclear weapons.