(AP) - Former President Clinton, setting aside his own criticism and ambivalence, issued a full-throated endorsementWednesday of Barack Obama as a leader ready to confront anychallenge.

Clinton was trying to roll back a line of attack made by him and his wife in their primary battle, and taken up now by John McCain,the presumptive Republican presidential nominee. McCain unloaded anew TV ad that contended Obama is "dangerously unprepared" forthe White House.

Another McCain ad appropriated one of Hillary Rodham Clinton'sown attack spots on Obama, one that showed sleeping children and a3 a.m. phone call into the White House portending a crisis. Itsuggests Obama doesn't have the experience to rise to a challenge of that sort.

Clinton's prime-time speech argued forcefully that Obama is prepared for the domestic, foreign and national security challenges that will arise in the coming years.

The wide-ranging speech also focused onDemocrats' policy achievements, including Clinton's own.

And it emphasized the need to elect a Democrat to the WhiteHouse "to restore America's standing to what it was eight yearsago."

Clinton's challenge was all the taller because he himself hadquestioned Obama's credentials.

During the primary race, the former president tried to raisedoubts about whether the first-term U.S. senator from Illinois had theexperience to lead the country. He said Obama's opposition to theIraq war was a "fairy tale."

Last fall, he dismissed Obama as totally unqualified.

"I mean, when is the last time we elected a president based onone year of service in the Senate before he started running?"Clinton said on "The Charlie Rose Show." "In theory, we could findsomeone who is a gifted television commentator and let them run."

Last winter, Clinton said that after "all the mean things" theObama campaign had said about him, "I should be the last person todefend him. [But] if he wins this nomination, I'm going to do whatI can to help him win."

Yet since Obama clinched the nomination in June, Clinton hasseemed less than passionate about an Obama presidency, giving onlylukewarm endorsements.

The ex-president has experience at the task of endorsing,passing the torch and then getting out of the way.

At the 2000 Democratic convention, Clinton boasted of hisachievements and asked voters to help elect his understudy Al Goreas his successor. He ignited a frenzied celebration.

Bill Clinton endorses Obama at Democratic National Convention