"This time last week, Moon was coming here with the intention of trying to heavily script what Trump would do in his meeting with Kim," said Victor Cha, a National Security Council official in the George W. Bush Administration. "Now, he's coming here just to try to save the summit. The mission has really changed."
For Moon, who has staked his presidency on the peace push, the White House visit represents a crucial opportunity to soothe Trump's concerns and, perhaps, readjust his expectations.
"I think that Trump imagined he would go into this meeting and be able to have a historic breakthrough with a deal, but it's clear he's starting to realise it won't be as easy as he imagined," said Jean Lee, director of the North Korea programme at the Woodrow Wilson Centre.
Going into the North Korea meeting, senior Administration officials say, the President has been almost singularly focused on the pageantry of the summit. He has not been deeply engaged in briefing materials on North Korea's nuclear programme, said three people with knowledge of the White House efforts.
Trump, who has pitched himself as the ultimate negotiator, has focused on ambitious deals as President but has struggled with the fine print.
He just hit the pause button on his threatened trade war with China, announcing an agreement to reduce America's trade deficit with China - but few details. And his Middle East peace plan is months overdue and facing a more sceptical audience than ever.
He recently withdrew the US from the international Iran-nuclear deal - without outlining future goals with his allies.
Many European officials have chafed at the Trump Administration's positions on Iran, the Paris climate accord, moving the US Embassy in Israel to Jerusalem, and trade tariffs.
Yesterday US Secretary of State Mike Pompeo launched a sweeping broadside against the Iranian Government, vowing to use all US economic and military might to destroy its economy and "crush" its operatives and proxies around the world. State Department officials said the aim of the speech was to outline a path forward.
Pompeo's plan would start with "unprecedented financial pressure" aimed at getting Iran back to the negotiating table. Pompeo listed a dozen demands, an agenda encompassing Iran's foreign ventures as well as its nuclear and missile programmes. If Iran agrees to those demands, he said, the US would lift all sanctions, re-establish diplomatic relations with Tehran and provide it access to advanced technology.
Pompeo said he will work with the Defence Department and regional allies to "deter Iranian aggression" in the region, including at sea and in cyberspace. "We will ensure freedom of navigation on the waters in the region. We will work to prevent and counteract any Iranian malign cyberactivity. We will track down Iranian operatives and their Hizbollah proxies operating around the world and crush them. Iran will never again have carte blanche to dominate the Middle East."
Iranian President Hassan Rouhani promptly rejected Pompeo's assertion and declared the era of US domination "over". He said: "Who are you to decide for Iran and the world? The world today does not accept America to decide for the world, as countries are independent."
The suggestion of a further US military role in the region was striking, since Trump has said he seeks to draw down the US troop presence in Syria, where Iran provides training and arms.
- AP, Washington Post, Telegraph Group Ltd
