LONDON — Keir Starmer has survived a political near-death experience. And he’s just the latest British prime minister to look shaky in the job. Less than two years after walking into No. 10 Downing Street, Britain’s leader is already facing calls to quit from his own party — and embarking on yet another reset of his operation to try to turn things around. His recent predecessors as prime minister may have some sympathy. Former Conservative Prime Minister David Cameron’s sudden departure from No.