A sore loser or a potent advocate, it's time for Bill to make up his mind

It'll be terrific on the night. With Bill Clinton it always is. Far less certain is whether his convention speech tonight will lay to rest the lingering uncertainties about his involvement in the Obama campaign this autumn, his role in the party and – not least – his peace with himself.

Mr Clinton comes to the convention in the unaccustomed role of a loser, if only by association. He threw himself into his wife's campaign, but she was outsmarted by an upstart rival, peddling "fairy tales" according to the former president, but who proved that he was more than a match for the most vaunted machine in Democratic politics.

By all accounts Mr Clinton and the young man bidding for the job he held have hardly spoken since the end of the epic primary battle. His public support has been lukewarm at best. Was Mr Obama ready to be president, Mr Clinton was asked last month. No one could ever be prepared for the job beforehand, was the most ringing endorsement he could muster.

Tonight the support will be more full-throated – as it has to be before an audience still divided by the primary battle, but determined not to blow an election in circumstances that could not be more favourable. The grievances however, will surely linger.

There are several. The ex-president, whose empathy with African Americans once earned him the description of America's first "black" president, still fumes at accusations that his blundering on the race issue played into Mr Obama's hands in the South Carolina primary and elsewhere.

He is said to be miffed that tonight he is scheduled to speak during a session devoted to international affairs, instead of economic policy where he believes he excelled. Mr Obama's response to a question about the arrangements also hinted at a coolness between the two. "I would never dream of censoring Bill Clinton," he said – but without a smile.

What may rankle most however is what to this proud, self-absorbed man is the whipper-snapper's apparent belittling of his achievement in office. Whether you agreed with him or not, Mr Obama remarked during a campaign debate, Ronald Reagan had been a "consequential" president. The implication was that Mr Clinton had not been.

Only 62, Mr Clinton faces the problem common to all active former presidents: what to do as an encore after you've held the most powerful job in the world? Jimmy Carter seems to have found a satisfying solution, but he has not. The last Democratic president has focused on international development and aid. But his elder statesman's role has been impaired by campaign 2008 – not so much because of his efforts on behalf of his wife, but for the scant grace with which he has taken her defeat.

Mr Obama could have no more potent advocate on the stump than an enthusiastic Bill Clinton. But a lukewarm Bill Clinton would only reinforce suspicions that secretly he would prefer Mr Obama to lose this time, opening the way for a second Hillary run in 2012.

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