Conceding that many struggling in a slow-recovery economy don't yet feel the change, Clinton said in a prime-time speech that circumstances are improving "and if you'll renew the president's contract you will feel it."
To the cheers of thousands of Democrats packed into their convention hall, he said of Obama, "I want to nominate a man who is cool on the outside but who burns for America on the inside."
The speech was vintage Clinton, overlong for sure, insults delivered with a folksy grin, references to his own time in office and his wife Hillary, all designed to improve Obama's chances for re-election in an era of painfully slow economic growth and 8.3 percent unemployment.
Clinton spoke as Obama's high command worked to control the political fallout from an embarrassing retreat on the party platform, just two months from Election Day in a tight race with Republican challenger Mitt Romney.
Under criticism from Romney, the Obama camp abruptly rewrote the day-old document to insert a reference to God and to declare that Jerusalem "is and will remain the capital of Israel." Some delegates objected loudly, but Los Angeles Mayor Antonio Villaraigosa, presiding in the largely-empty hall, ruled them outvoted. White House aides said Obama had personally ordered the changes, but they did not disclose whether he had approved the earlier version.
The convention hall rocked with delegates' applause and cheers as Clinton - unofficial Democratic ambassador-in-chief to anxious voters in a tough economy - strode onstage to sounds of "Don't Stop Thinking About Tomorrow," his 1992 campaign theme song.
He sought to rebut every major criticism Republicans have leveled against the president at their own convention last week in Tampa, and said that in fact, since 1961, far more jobs have been created under Democratic presidents than when Republicans sat in the White House - by a margin of 42 million to 24 million.
Clinton accused Republicans of proposing "the same old policies that got us into trouble in the first place" and led to a near financial meltdown. Those, he said, include efforts to provide "tax cuts for higher-income Americans, more money for defense than the Pentagon wants and ... deep cuts on programs that help the middle class and poor children."
"As another president once said, 'There they go again,'" he said, quoting Ronald Reagan, who often uttered the remark as a rebuke to Democrats.
Obama flew into his convention city earlier in the day and arrived in the hall for Clinton's speech. He arranged to join the former president onstage afterward in a made-for-television joint appearance."In Tampa the Republican argument against the president's re-election was pretty simple: 'We left him a total mess, he hasn't finished cleaning it up yet, so fire him and put us back in,'" Clinton said.
"I like the argument for President Obama's re-election a lot better. He inherited a deeply damaged economy, put a floor under the crash, began the long hard road to recovery and laid the foundation for a more modern, more well-balanced economy that will produce millions of good new jobs, vibrant new businesses, and lots of new wealth for the innovators."
On an unsettled convention day, aides scrapped plans for the president to speak to a huge crowd in a 74,000 seat football stadium, citing the threat of bad weather in a city that has been pelted by heavy downpours in recent days.
"We can't do anything about the rain. The important thing is the speech," said Washington Rey, a delegate from Sumter, S.C.
That and the eight-week general election campaign about to begin between Obama and Republican challenger Romney, who spent his second straight day in Vermont preparing for this fall's debates with Obama.
Clinton shared prime time with Elizabeth Warren, the Democratic candidate for a Republican-held Senate seat in Romney's Massachusetts. For many years "our middle class has been chipped, squeezed and hammered," she said.
In a tight race for the White House and with control of the Senate at stake, Democrats signaled unmistakable concern about the growing financial disadvantage they confront. Officials said Chicago Mayor Rahm Emanuel, who was Obama's first White House chief of staff, was resigning as national co-chair of the president's campaign to help raise money for a super PAC that supports the his re-election.
Unlike candidates, outside groups can solicit donations of unlimited size from donors. At the same time, federal law bars coordination with the campaigns.
Inside the hall, a parade of speakers praised Obama and criticized the Republicans, sometimes harshly.
Sandra Fluke, a law student whom congressional Republicans would not let testify at a hearing on contraceptives, said if Republicans win in the fall, women will wake up to "an America in which access to birth control is controlled by people who will never use it, in which politicians redefine rape."
Clinton's speech marked the seventh consecutive convention he has spoken to party delegates, and the latest twist in a relationship with Obama that has veered from frosty to friendly. The two men clashed in 2008, when Obama outran Hillary Rodham Clinton's wife for the Democratic presidential nomination.
Clinton, then a New York senator, now Obama's Secretary of State, was in East Timor as the party met half a world away. She made a cameo appearance on the huge screens inside the Time Warner Cable Arena, though, turning up in a video that celebrated the 12 Democratic women senators currently in office.
Whatever the past differences between presidents current and past, Obama and his top aides looked to Clinton as the man best able to vouch for him when it comes to the economy, his largest impediment to re-election.
As a group, white men favor Romney over Obama, according to numerous polls, but a Gallup survey taken in July showed 63 percent of them view the former president favorably, to 32 percent who see him in unfavorable terms.
Republicans have suddenly discovered a lot to like about Clinton - a man they impeached in late 1998 when they ran the House and he sat in the Oval Office.
Ryan made no mention of those unpleasantries when he told a campaign audience in Iowa, "Under President Clinton we got welfare reform. President Obama is rolling back welfare reform.
"President Clinton worked with Republicans in Congress to have a budget agreement to cut spending. President Obama, a gusher of new spending."
Independent fact checkers have repeatedly debunked the claim about Obama's welfare proposals. Nor did the Wisconsin lawmaker mention that under a balanced budget compromise with Clinton to rein in federal spending, Republicans agreed to create a new benefit program that provides health care for lower-income children and others ineligible for Medicaid.
The changes in the platform came after the Republicans criticized an earlier decision to strip out a reference to God.
Romney said that "suggests a party that is increasingly out of touch with the mainstream of the American people. ... I think this party is veering further and further away into an extreme wing that Americans don't recognize."
Romney had declared in a summertime trip there that Jerusalem was the country's capital. U.S. policy for years has held that the city's status is a matter for negotiations between Palestinians and Israelis, and Democrats said at the time he was pandering to Jewish voters in the United States.
The switch puts the platform in line with what advisers say is the president's personal view, if not the policy of his administration. "Jerusalem is and will remain the capital of Israel," it says. "The parties have agreed that Jerusalem is a matter for final status negotiations. It should remain an undivided city accessible to people of all faiths."
Associated Press writers Jennifer Agiesta and Jack Gillum in Washington, Kasie Hunt in Vermont, Thomas Beaumont and Steve Peoples in Iowa and Ken Thomas, Matt Michaels and Jim Kuhnhenn in Charlotte contributed.