Washington, April 26, 2018 (News agencies) -- Emmanuel Macron conceded he had probably failed in his attempt during a three-day trip to Washington to persuade Donald Trump to stay in the Iran nuclear deal, describing US flip-flopping on international agreements as "insane". The French president had hoped to convince Trump to continue to waive sanctions on Iran, as agreed by the 2015 nuclear deal, in which Iran agreed to accept strict curbs on its nuclear activities. Macron offered Trump the prospect of negotiations on a new complementary deal that would address Iranian missile development and Tehran's military intervention in the Middle East. But speaking to US reporters before leaving Washington, Macron said: "My view – I don't know what your president will decide – is that he will get rid of this deal on his own, for domestic reasons." Noting that Trump had also pulled the US out of the Paris climate change accord – another commitment of the Obama administration – Macron said such frequent changes in the US position on global issues "can work in the short term but it's very insane in the medium to long term". The admissions come after a day of intimate fraternity with Trump, during which Macron made an impassioned speech in Washington advocating many of the things Trump has spent much of his presidency trying to destroy. Over the course of a 50-minute address to a joint meeting of Congress on Wednesday, the French president said he was "sure" the US would one day return to the Paris climate change accord, and vowed that France would not abandon the 2015 nuclear deal with Iran, known as the Joint Comprehensive Programme of Action (JCPOA) He had an even more direct rebuke for his host's resort to tariffs as an instrument of trade policy. Macron said that the right way to correct trade imbalances and overcapacity was to negotiate through the World Trade Organisation. On the Iran nuclear agreement, Macron repeated an idea he had promoted on Tuesday at a White House meeting with Trump for a "new deal" that would complement the 2015 accord with a broader remit to address Iranian ballistic missile development and its military role across the Middle East. Iran, Macron said would "never possess any nuclear weapons" but he added: "This policy should never lead us to war in the Middle East." He called for respect for the sovereignty of Iran and its ancient civilisation, and urged the west not to "repeat past mistakes", an apparent reference to the 2003 Iraq invasion. Both the US and France endorsed the JCPOA, he pointed out, adding: "We should not abandon it without something more substantial in its place." In a tweet after his speech to Congress, Macron added: "We decided with President [Trump] to work on a new comprehensive deal" which would address Iranian missiles and its regional role, and make limits on Iranian nuclear activities permanent.