• Morgan McSweeney has resigned as chief of staff to UK Prime Minister Keir Starmer.
• His resignation follows the controversy over Peter Mandelson's appointment as US ambassador.
• Documents revealing Mandelson's ties to Jeffrey Epstein intensified scrutiny on Starmer's judgment.
• McSweeney took full responsibility for advising Starmer on Mandelson's appointment.
• The incident has triggered a political crisis within the Labour Party.

Morgan McSweeney has resigned as chief of staff to British Prime Minister Keir Starmer, citing the controversial appointment of Peter Mandelson as the UK ambassador to the United States. McSweeney stated that "the decision to appoint Peter Mandelson was wrong" and acknowledged the damage it caused to trust in the political system. His resignation is seen as a significant political fallout from this controversy, marking a critical point in Starmer's premiership, which has been under increasing scrutiny over this issue. This crisis has been described as the most serious challenge Starmer faced during his time in office according to SCMP, India Times, and BBC.

The controversy erupted following the release of documents from the US Justice Department that detailed Mandelson's relationships and alleged misconduct involving Jeffrey Epstein. It was reported that Mandelson had previously leaked sensitive information to Epstein during his tenure as business secretary, leading to a police investigation into his actions while in public office. McSweeney, who played a key role in Starmer's ascent to leadership, noted the gravity of the situation, declaring he takes full responsibility for advising the Prime Minister on the appointment. This act of resignation points to broader questions regarding Starmer's judgment and leadership capabilities, as noted by multiple sources including India Times and BBC.

As a result of McSweeney's departure, Starmer faces mounting pressure from within the Labour Party, where some members have openly called for his resignation due to the mishandling of the Mandelson appointment. Starmer expressed that working with McSweeney had been an "honour" and acknowledged the support McSweeney provided during challenging times. However, the political landscape in the Labour Party is becoming increasingly turbulent, with dissent regarding Starmer's decision-making now at the forefront, as indicated by reactions from various political pundits and MPs reported by India Times and BBC.