Past presidents often accomplished nothing using traditional negotiations. Even when they made deals, the opposite side broke them, like nuclear agreements with North Korea or NATO defense payment promises. Trump can make a stink of things to force situations. At least he tries a new way. His personal meetings with Kim has gotten them to stop setting off nuke explosion, released American prisoners they were holding, and stopped intercontinental missile testing. That's not bad.
As far as Iran, there was no treaty. The Senate never approved the agreement as required by our constitution. And Obama knew he wouldn't get Senate approval so he never submitted it to them for approval. Iran knew that. But Iran rolled the dice anyway and it came up craps. If they negotiate with Trump or any president, they'll knew next time to insist upon Senate approval so it's a formal treaty. Then subsequent president can't cancel them without Senate approval.
From Kim Trump has got 'warm letters', nothing more.
Iran could do the same to please Trump, but they won't of course...
Iran just breached the nuclear limit because of Trump breaking the deal one year earlier. A deal that many countries including the US had worked on for years and that was working well.
Iran was kept under surveillance all the time and they never breached the deal.
But now, one year later, they cannot ignore the sanctions they got to handle, sanctions that are making their economy far worse.
Europe does not dare to keep their (trade) promises to Iran because they know trading with the US is more important.
History shows that Iran 'never' ( centuries) started a war... On the contrary ; they were under attack by Saddams Irak that carried western weapons.
This could happen again.
The USA under Trump has made the Middle East a more dangerous place, by trading enormous amounts of weapons to Saudi Arabia ( for what purpose?) and by choosing openly the Israelian site in the conflict with the Palestines. His name will be given to one of the many illegal settlements in occupied territory to show Nethanyahu's gratitude.