On his first day back on the campaign trail after a brief hiatus, John Kerry (search) Thursday received the endorsement of former rival Howard Dean (search) and others who are putting aside their differences to unite behind the Massachusetts senator in an effort to oust President Bush from the White House.

"We had a tough campaign here," Dean said as he endorsed Kerry at a rally at George Washington University. "It is tough. We're both tough competitors. But there are things in the campaign we talked about focusing on the things that divide us. Now we are going to talk about the things that we have in common."

Meanwhile, Bush headed to New Hampshire and Massachusetts to highlight his plans for retraining laid-off workers and accuse Kerry of pushing higher taxes.

Bush's appearance in Nashua, N.H., follows a two-year span in which New Hampshire lost 17.8 percent of its manufacturing jobs, the greatest percentage decline for any state in the country, or about 18,000 jobs.

The foray into Boston is for a $2,000-per-person fund-raiser for a re-election campaign that has raised $170 million. A Boston fund-raiser by Vice President Dick Cheney brought in $1.2 million last June.

In Nashua, the president defended himself against recent accusations that he didn't do enough to prevent the Sept. 11, 2001, terror attacks.

"Had I known that the enemy was going to use airplanes to strike America, to attack us, I would use every resource, every asset, every power of this government to protect the American people," Bush said, drawing applause.

Dean pledged to use his new grass-roots organization for Kerry's bid and said the country would be devastated by another four years of what he called a "right-wing ideological agenda" and weak leadership.

Despite the glaring differences between the two men earlier during the Democratic primary, Kerry said when they met prior to the endorsement, "we indeed looked for the differences, but I tell you something, that we had to look hard for the differences."

Kerry also challenged the incumbent to debates in six states.

"After more than three years of broken promises and failed policies, America needs a new direction — so the stakes could not be higher in this election," Kerry said. "President Bush — if the attack ads can start now, so can the debates about the issues that matter."

The four-term senator specifically wants debates with Bush on: national security, homeland security and veterans in Pennsylvania; creating jobs and rebuilding the economy in Ohio; education in Arizona; health care in Missouri; energy and the environment in Washington; and equal opportunity in Florida.

The American Federation of State, County and Municipal Employees (search) also endorsed Kerry after a meeting of the union's executive council. With 1.3 million members, AFSCME is the second-largest union in the AFL-CIO (search) and boasts one of organized labor's largest and most savvy political operations.

"We are proud to support a candidate who will stand up for America's workers, fight to keep good-paying jobs here in the United States and make sure every American has access to affordable healthcare," said President Gerald McEntee. "With John Kerry, we can take back the White House from a president who works for the corporations and the very rich instead of working families."

He added that AFSCME will run its "most aggressive member mobilization program ever."

Kerry and Democratic National Committee chairman Terry McAuliffe (search) also said the party, with $25 million and no debt, was better prepared than ever before to challenge the GOP and its incumbent president.

"The tools are in place," McAuliffe told the National Newspaper Publishers Association (search), which represents black newspapers around the country. "Now we need to make sure to use these tools to make sure that John Kerry is elected president."

McAuliffe promised the publishers that the DNC would buy advertising in the black press, and Kerry said he embraced the commitment to advertise in black newspapers.

"I am determined that in this election, in this race, during the course of our campaign, we're going to reach out in an unprecedented fashion," Kerry said. "We are asking you to engage in an unprecedented way. We need to build the greatest grass-roots movement in the history of this country."

Kerry met privately with Dean's congressional supporters and donors before accepting an endorsement from the former Vermont governor, who was a bitter critic of Kerry during the campaign.

AFSCME initially endorsed Dean, but McEntee withdrew support last month after the former Vermont governor failed to win a presidential primary or caucus.

Kerry's first day back on the campaign trail will end with a fund-raiser attended by top Democrats acknowledging Kerry's new status as head of the party. About $11 million is expected to be raised for the DNC.

Former Presidents Carter and Clinton, 2000 Democratic nominee Al Gore, and all of Kerry's primary rivals, except Dennis Kucinich and Carol Moseley Braun, are expected to join the celebration.

In the coming days, Kerry plans a series of speeches to outline his key campaign issues and differences with Bush. He delivers the first speech on Friday in Detroit, which aides billed as a major policy address dealing with jobs, Kerry's plans to create them and his critique of Bush for presiding over the loss of more than 2.2 million jobs.

Aides said Kerry would give at least three speeches focusing on economic issues, the area where Kerry believes he can make inroads against Bush. Polls show a tight race between Bush and Kerry, with the senator doing best on domestic, economic matters and the Republican incumbent strongest on national security and fighting terrorism.

Kerry had been largely out of public view for the better part of a week as he and his wife, Teresa Heinz Kerry (search), vacationed at their home in Ketchum, Idaho. He returned to Washington late Wednesday and told reporters traveling with him that he felt rejuvenated.

"No more long answers," Kerry said. "It doesn't take me long to recharge my batteries."

The Associated Press contributed to this report.