Nancy Pelosi, the speaker of the House of Representatives, helped buy Hillary Clinton some breathing space on Tuesday amid growing calls from senior supporters of Barack Obama for the former first lady to quit the Democratic party’s presidential race.

Mrs Pelosi, who is thought to sympathise with Mr Obama but who remains officially neutral, told ABC News that the primary race should “run its course”. The contest, which goes to Pennsylvania in three weeks – a contest Mrs Clinton needs to win by a significant margin – ends on June 3, when Montana and South Dakota hold nominating contests.