Monday briefing: How is it possible the prime minister didn’t know about Mandelson’s vetting failure?

UK Prime Minister Keir Starmer faces political backlash after it was revealed Peter Mandelson, appointed as ambassador to the US, failed UK security vetting without his knowledge. Starmer called the situation 'totally unacceptable' and is under pressure to resign, while other news includes a mass shooting in Louisiana and arrests linked to a theft plot targeting high-end stores.