An aide to Hillary Clinton who closely followed the 2010 negotiations which resulted in the Hillsborough Castle Agreement told the former American Secretary of State that David Cameron was "recklessly" threatening the Northern Ireland peace process at the time.
Clinton, who is the leading Democratic candidate for the party's presidential nomination, is releasing thousands of emails from her time as American Secretary of State.
She is doing so to dispel claims she jeopardised national security by using a personal email address and her own equipment rather than an email provided by the government which would have had added security.
The latest batch, released in November reveal the 68-year-old was briefed on the flag protests and Martin McGuinness's historic meeting with the Queen in Belfast.
The veteran politician was keen to know if Prince Philip also shook the former IRA commander's hand during the visit in the Lyric theatre, which he did.
Sidney Blumenthal, a close political aide to both Hillary and Bill Clinton, sent a series of emails on the then leader of the opposition, David Cameron's role in the political negotiations of 2010.
He detailed how the future Prime Minister was playing a "destructive role" in the talks as he chased down marginal seats in Northern Ireland by courting the UUP to secure majority government.
Blumenthal said the conservative leader was prepared to ruin all the work that had gone before in the peace process in a "desperate" attempt to hang on to a parliamentary seat in the run up to the 2010 general election.
In an email dated January 25, 2010, and with the subject 'latest in NI crisis negotiations', Blumenthal said: "Cameron has intervened, threatening recklessly to destroy a generation of work, in order potentially to gain marginal seats in NI in case of a hung parliament. Secret meetings were held at a country house of NI Unionists and Tories."
He enclosed an article from the Guardian, which he described as "highly accurate", which discussed the consternation caused by Cameron's intervention.
In February that year the Tories and the UUP launched their ultimately doomed UNCUNF partnership.
Then in March the UUP made a series of last minute demands that threatened to derail the Hillsborough talks.
Blumenthal wrote that he was furious with Mr Cameron and the Conservative Party. He described the UUP leader, Reg Empey's demands as ultimately irrational and self-destructive.
In March 4, 2010 he wrote: "The motives behind (UUP leader Reg) Empey's and the UUP's intransigence are complex, ultimately irrational and self-destructive.
"While Empey has been lured down this primrose path by Cameron's alliance, Cameron now, publicly at least, supports the peace process, though too softly in private. Despite the supposed promise of benefit from allying with the supposed inevitable Cameron government, the politics are not at all what they seem on the surface."
Clinton was kept well-informed of the political dealing in Northern Ireland and was constantly sent news reports by her aide.
The then Secretary of State Shaun Woodward - in an email marked confidential - was said to have encouraged former American President George W Bush to contact Cameron.
In the subsequent call, Bush impressed upon Cameron the importance of the UUP to be a part of any talks resolution.
In a March 6 email, ahead of an Assembly vote on the talks deal, the advisor said Empey was trying to make Peter Robinson's life "impossible".
"Empey finally produced a document laying out the UUP position," he wrote.
"Among its demands was one for reorganization of the executive, conceived to undermine the process. Robinson and McGuinness, in fact, have already asked Empey to head a commission to make recommendations on making the executive work better.
"Robinson has told Shaun he is prepared to help Empey on the education issue, but not if he is unwilling to help on the peace process.
"Empey is also making a demand about who can be the justice minister that Shaun characterizes as 'insane'."
He continued: "It is unclear what is going on with Cameron. Is he actually pushing for the agreement or not? If he is, does he have any influence?
"Either Cameron is purposefully not being strong with Empey or he is being spurned, making calls.
"If he is not really pressuring Empey, it would be out of a desperate and vain attempt to grab a parliamentary seat in the case of a hung parliament—a seat that is out of his grasp.
The seat referred to was that of North Down MP Sylvia Hermon's. She quit the party over its links to the Conservatives in 2010 ahead of the election and retained the seat in the May vote.
Blumenthal predicted disaster for the UUP if they were not on board for any subsequent deal, he added: "There is a prospect that Empey's failure to endorse might not produce meltdown. If so, that would toll the end of the UUP. Having tried to wreck the agreement, they would be left stranded."
He later said that the UUP leader was doing "everything" he could to wreck the Hillsborough Castle agreement.
Clinton herself in one email quipped that the UUP leader probably saw the glass as "half empey".
After the Assembly voted in favour of the Hillsborough Castle agreement, without the support of the UUP, Blumenthal laid blame at the door of the Tories.
He said: "Cameron and the Tories have played a wrecking role. Cameron cares more about getting a few parliamentary seats for a majority by an alliance with the Unionists than the peace process.
"Having made that alliance he will be prisoner to it. It goes without saying (though I'll say it) that you've been consistently lied to."