For all his recent troubles – his resounding loss in Pennsylvania 10 days ago, his inability to crack Hillary Clinton's hold on white, working class voters and, of course, the Reverend Jeremiah Wright chronicles – Barack Obama still seems to be winning the battle that really counts: the one for superdelegates.

Harvesting superdelegates is now more important than ever since they will almost certainly determine who wins the nomination at, or before, the Democratic National Convention in August. And yesterday saw a defection that serves to underline that garnering superdelegates is an area where Mr Obama is still doing surprisingly well.

Joe Andrew, a former leader of the Democratic Party and a native of Indiana, announced he was flipping from Mrs Clinton's side and now supports Mr Obama.

Download the new Independent Premium app Sharing the full story, not just the headlines

That switch alone should be an important boost to the Obama campaign. Appointed as chairman of the Democratic National Committee in the waning days of Bill Clinton's presidency, Mr Andrew declared his support for Mrs Clinton on the day she announced she was running for president.

But in a letter to party members in Indiana and in media interviews, Mr Andrew said he was jumping the fence because he felt "inspired" by Mr Obama and he urged Indiana voters to join him in the state's primary on Tuesday.

In particular, he cited the manner in which Mr Obama has handled the continuing flap over the Rev. Wright controversy, as well as his refusal to join Mrs Clinton and Republican nominee John McCain in calling for a suspension of the federal tax on petrol on the grounds that it is a political gimmick.

"He has shown such mettle under fire," Mr Andrew said. "The Jeremiah Wright controversy just reconfirmed for me, as the gas tax controversy confirmed for me, that he is the right candidate for our party." He also said that voting for Mrs Clinton, who faces almost insurmountable odds in collecting enough convention delegates actually to win, will only prolong a process that is hurting the party.

"The math[ematics] for this is simple," Mr Andrew told ABC News. "A vote for Hillary Clinton is a vote to continue this process." If Mr Obama can carry both Indiana and North Carolina on Tuesday – he is ahead in the latter but appears to be in a close race in the former – it could be enough to force Mrs Clinton out.

A CBS-New York Times poll offered mixed news for Mr Obama. On the one hand, it showed him leading Mrs Clinton by eight points among Democratic voters nationally, an improvement over early April when the same survey saw him holding only a three-point edge.

But on the other hand, any notion of inevitability for Mr Obama seems to have evaporated. A month ago, 69 per cent of Democrats said they thought the nomination would be his. That number has shrunk to 51 per cent, reflecting the damage done by his recent losses and the Wright saga.

There would be outright panic in the Obama camp if the bumps of recent weeks were translating into a rush of so-far uncommitted superdelegates to Mrs Clinton. But, to date, the opposite seems to be happening. His net gain in superdelegates just yesterday morning: 4. Her net gain: 0.

Mrs Clinton is winning a few, most notably the endorsement of North Carolina Governor Mike Easley earlier this week. But in two months, the most recent estimates show that Mr Obama has halved Mrs Clinton's previously healthy advantage in superdelegate pledges. Moreover, for the first time he has taken the lead over Mrs Clinton among superdelegates who are members of Congress.

For rolling comment on the US election visit: independent.co.uk/campaign08