Barack Obama on Thursday became the first American presidential candidate since Richard Nixon to rely solely on private money to sustain his White House bid when he declared that he would opt out of the Watergate-era public financing system.

Mr Obama’s decision, which he announced to supporters in a webcast, was met with strong criticism from John McCain, his Republican opponent who will rely on the $84m in public funds that are available, and also from centre-left reformers who said they felt bitterly betrayed by his move.