Expert consensus, although far from unanimous, is that his move has made the world more dangerous. Most mainstream media in the United States take a similar view. The New York Times calls it vandalism.
Amid wholesale condemnation, and obvious flaws in Mr Trump's reasoning, it is worth pausing to note the deal he jettisons has its limitations. Despite assurances, the intrusive monitoring of what Iran is up to is far from perfect. Iran is able still to proceed with ballistic-missile development crucial for nuclear delivery and deterrence, and the agreement's sunset clauses leave open the option for resumption of research.
As well, logic says Iran would not have agreed to the deal if there was insufficient wriggle room. Its leaders will be aware, just as North Korea's Kim Jong-un knows, that having nuclear warheads means you are treated with caution, even respect. If Saddam Hussein had had nuclear weapons, the 2003 invasion of Iraq might never have happened.
Nonetheless, the agreement considerably slowed progress towards Iran's nuclear ambitions and was agreed to by the US' European allies of Germany, France and Britain, along with China and Russia. In a way, it bolstered the Iranian regime because it took a little pressure off the country's dire economic state. Frozen assets were released and increased foreign trade and business has taken place.
But the deal itself was unpopular among ''hardliners'' in Iran. They again can point, this time legitimately, to the perfidy of the United States. Their hand is strengthened.
Israel and Saudi Arabia are also pleased with Mr Trump. This line-up inspires additional concern rather than confidence.
Mr Trump's blunt and brutal negotiating can sometimes be effective. It has led to talks with North Korea. But Mr Trump has also signalled that the United States is an arrogant nation that fails to keep its word on agreements. Faith and trust everywhere in the world's most powerful country are further undermined. Europe's premier leaders, meanwhile, have been sidelined, despite their pleas.
In a dream outcome, a tighter new agreement would be negotiated and the United States would not proceed with sanctions and other measures. But it took years and vigorous efforts from many quarters to secure the previous deal. More likely is a nightmare where Iran gives up on co-operation and powers ahead to become a nuclear power as fast as it can.
World affairs are often messy, so in-between results and other unpredictable consequences are possible. More unpredictability and more instability are not what the world needs.
Typically, Mr Trump has not come up with any specifics on how the current deal could be replaced.
He threatens and blusters. He would impose the ''highest level of sanctions'' and warned other countries of violating US law.
But if other nations, including his erstwhile allies, continue to deal with Iran and import its oil, can the United States slap secondary sanctions on various countries and their companies? Imagine what that would do to diplomatic and trade tensions.
Will European countries, and the likes of little New Zealand, grudgingly go along with Mr Trump and retighten conditions on Iran? How will Russia and China exploit the new situation?
It is so hard to see good coming from Mr Trump's bombast and hectoring and his black-and-white, simplistic stance on complex affairs and relationships. He has scuppered a hard-fought-for agreement, shown disregard for trust in the word of the US and sundered from European allies.
Iran, it would now appear, will be freer to pursue nuclear plans. The world becomes more dangerous and volatile.
