The Republican field is rapidly being winnowed out as Mr Bush advances. Dan Quayle, the hapless former vice-president, was due to announce yesterday that he was pulling out because of the shortfall in his resources. Mr Quayle was the deputy to Governor Bush's father, George Bush, but none the less the party seems to have decided that his case for the candidacy was not strong enough.
Mr Quayle believed that it was his turn, but no one else did, apparently.
Mr McCain comes in third in most opinion polls of likely Republican voters. He has positioned himself as a moderate, campaigning against tobacco and for reform of America's campaign finance laws.
He is much loved by the media as a straight talker and a man of principle. He is a Vietnam veteran and a former prisoner of war in a Hanoi jail, with strong appeal for other veterans. But none of this has been enough so far to lift him above Mr Bush. Even the governor of his own state, Arizona, will back Mr Bush.
Mr McCain said yesterday: "It is because I owe America more than she has ever owed me that I am a candidate for president of the United States."He spoke of how American government had become "a spectacle of selfish ambition". He contrasted his own experience with Mr Bush's youth. "There comes a time when our nation's leader can no longer rely on briefing books and talking points, when the experts and the advisers have all weighed in, when the sum total of one's life becomes the foundation from which he or she makes the decisions that determine the future of our democracy," he said.
Mr McCain will skip the Iowa caucuses and campaign heavily in New Hampshire, South Carolina and Arizona, states where he believes he has a strong chance of winning.
With Mr Quayle's departure, there are now seven candidates chasing the Republican slot: Mr Bush, Mr McCain, Elizabeth Dole, who comes second in most polls, Steve Forbes, the billionaire publisher, Gary Bauer, a social conservative, Allan Keyes, a broadcaster and former Reagan administration official, and Senator Orrin Hatch. Pat Buchanan, the party's nationalist maverick, seems set to leave for the Reform party.