Democratic presidential hopeful Barack Obama finally wrested his convention away from the Clintons and opened the assault on Republican John McCain that Democratic leaders had been demanding.

Mr Obama and his supporters spent the better part of two days of a four-day national convention dealing with the Clintons, Hillary and Bill, using up time that might have been better spent defining their rival Mr McCain.

In the end, they succeeded by achieving some measure of party unity, with both Clintons giving rousing speeches on Mr Obama's behalf despite tensions remaining from his defeat of Hillary Clinton in a bruising battle for the party nomination.

"It seemed to me that the Clintons did what they needed to do," said Democratic strategist Jim Duffy.

"But it does also seem like the last two days were more about them than him."

When Mr Obama's turn came to address his convention, he did so before a crowd of about 75,000 supporters at the Denver Broncos' pro football stadium, standing in front of mock Greek-style pillars that gave the evening a rock concert feel.

Republicans called the big show an act of hubris expected of a candidate they denounce as a celebrity, but the stadium gamble allowed Mr Obama campaign to offer some powerful imagery for Americans and draw a big Colorado crowd in a state considered an important battleground in the November 4 election.

Urged by Democratic leaders to toughen up the attacks on Mr McCain, Mr Obama did just that, calling him out of touch, an acolyte of unpopular Republican President George W. Bush and misguided on foreign policy.

Mr Obama attacked a central premise of Mr McCain's campaign, that Mr McCain is a foreign policy expert needed in a dangerous world.

His tendency to concentrate on the Iraq war more than on Afghanistan is wrong, Mr Obama said, slamming Mr McCain with a phrase Mr McCain likes to use about chasing down al Qaeda leader Osama bin Laden.

"John McCain likes to say that he'll follow bin Laden to the Gates of Hell - but he won't even go to the cave where he lives,"Mr Obama said.

Larry Sabato, a political science professor at the University of Virginia, said he would rank the Democrats' 2008 convention about in the middle of the 17 of both parties he has attended, and that given four days to define McCain, this was done in only two of those days.

"They were able to make Mr Obama more acceptable and to restore some measure of party unity, but they never defined John McCain in terms that will help them in the fall," Mr Sabato said.

Republicans felt Mr McCain got off relatively easy.

"I think Mr McCain was able to, thanks to the Clintons, successfully not be the pinata this week,"

said Republican strategist Scott Reed.

Indeed, some speakers spent more time settling scores with the Bush-Cheney administration, including the two candidates who lost to Mr Bush, Mr Al Gore in 2000 and John Kerry in 2004.

Speaking on Wednesday night, Mr Kerry reviled the tactics that ex-Bush aide Karl Rove had used against him and warned these same tactics were being used by Mr McCain, who has populated his campaign with some former Bush aides.

"Senator McCain, who once railed against the smears of Karl Rove when he was the target, has morphed into candidate Mr McCain who is using the same Rove tactics and the same Rove staff to repeat the same old politics of fear and smear. Well, not this year, not this time," Mr Kerry said.

Mr Gore, who many Democrats believe should have won the disputed 2000 election, stood in the stadium on Thursday and outlined what might have been if he had won.

"Take it from me, if it had ended differently, we would not be bogged down in Iraq, we would have pursued bin Laden until we captured him," Mr Gore said.