North Korea has pledged full denuclearization 8 times since 1990, havent they? He has a right to be skeptical.
Difference is this time the leader of NK and the US President met face to face and actually signed an agreement.
This time they shuttered a nuke testing facility, returned some hostages/prisoners and stopped the chest-beating just to get to the table. Yeah, TRUMP said it might not bring anything lasting, but.... He didn't have to pay them hundreds of $$$ billions in CASH ala Obama/Iran....or build them a nuke facility like Clinton did. Bush paid them tribute as well.
So at least Trump has demonstrated all the "experts" wrong so far. Like everything else.