Hillary Clinton was repeatedly warned by a key confidant that the UK's Conservative-Liberal Democrat coalition would rapidly fall apart in the wake of the 2010 general election, according to newly released emails.
Sidney Blumenthal, an unofficial adviser to Mrs Clinton, delivered a withering assessment of the then-new government, describing foreign secretary William Hague as "disingenuous" and accusing deputy prime minister Nick Clegg of "inbred arrogance".
His comments are contained in the latest tranche of Mrs Clinton's emails to be released under US freedom of information laws after it emerged that she used a private server for government business when she was US secretary of state.
They show that she responded enthusiastically, saying she had shared them with her husband, Bill - the former president - who thought they were "brilliant", adding "Keep 'em coming when you can."
In one email from June 2010, Mr Blumenthal said the coalition's spending cuts meant the UK had little to offer the US and suggested that David Cameron would live to regret his commitment to austerity.
"On economic policy, the UK is no partner and no bridge to Europe," he wrote. "At no other time since World War II have the US and UK governments been at such odds over international economics."
He added: "Cameron must be let alone to receive the consequences (within 18 months) of his ideologically driven economics."
In another message sent the previous month while the coalition negotiations were taking place, Mr Blumenthal said that whatever the shape of the government that emerged, it would be "remarkably weak, flimsy and fly apart within weeks".
He said that she needed to be prepared to deal with Mr Hague "who is deeply anti-European and will be disingenuous with you".
He described the mood within the Conservative Party as "acrid and anxious" with the "Tory moneyman" Lord Ashcroft - whom he described as "evil" - said to be furious at Mr Cameron's failure to secure an outright election victory.
On the Labour side, Mr Blumenthal said Lord Mandelson was playing a "cynical double game", plotting to replace David Miliband as foreign secretary if they managed to stay on in government while at the same time offering to support him if he ran for leader.
However, his strongest remarks were reserved for Mr Clegg, who he said was determined to form a coalition with the Conservatives, even while he was also in talks with Labour.
"His inner Tory magnetically draws him to his heritage," he wrote.
"Clegg has also misplayed almost every turn, presented with big chances and blowing them through a combination of inexperience ... and inbred arrogance (from no less a privileged background than Cameron, though seeming less snobbish because he went to Westminster instead of Eton and has a less pronounced upper class accent)."
The release also includes a rueful email from David Miliband, thanking Mrs Clinton for her support after he was defeated by his brother, Ed, in the election for the Labour leadership.
"Losing is tough. When you win the party members and MPs, doubly so. (When it's your brother...)," he wrote.