Kerry arrived in South Carolina on Thursday, which will hold one of seven primary elections and caucuses next week, and promptly received the backing of congressman Jim Clyburn.
Clyburn's decision is a new boost to the 60-year-old senator and a blow to rival John Edwards, who was born in the state and has been leading in opinion polls there.
At an appearance with Clyburn at a technical college just outside Columbia, Kerry kept up his attacks on Bush over the Iraq war and particularly job losses in the US economy, which have badly hit states like South Carolina.
The senator has made a stunning comeback in his bid to be the Democratic candidate to take on President George Bush in the 2 November presidential election, routing six rivals in the first two state votes.
All seven remaining Democratic candidates are due to take part in their first televised debate together since Kerry's victories and the Massachusetts senator is expected to become the new target.
Kerry also faces a major test in the so-called "Super Seven" votes on Tuesday, mainly in the southern states which are the home territory of rivals Senator John Edwards and retired four star general Wesley Clark.
Meanwhile, Howard Dean has replaced his campaign manager, Joe Trippi, mastermind of the former Vermont governor's Internet-fuelled rise to prominence last year.
He has also ordered spending cuts, following his third-place finish in Iowa and second place in New Hampshire this week.
"We are having to husband our resources," said Dean, who last year raised more money in one year than any Democratic presidential candidate in history.
"We are worried about money. We want to be careful about money. But we are not broke," Dean told reporters as he announced that Roy Neel, a former advisor to ex-vice president Al Gore, had been brought in as campaign manager.
"We had really geared up for what we thought was going to be a front-runner's campaign and it's not going to be a front-runner's campaign. But it's going to be a long, long war of attrition and we're now preparing for that"
Democratic presidential contender
Amid widespread concern about the health of his campaign, Dean has also asked staff to wait two weeks for their next salaries.
Dean said: "We had really geared up for what we thought was going to be a front-runner's campaign and it's not going to be a front-runner's campaign. But it's going to be a long, long war of attrition and we're now preparing for that."
Dean has always billed himself as an insurgent fighting the Washington establishment, but the appointment of Neel is a shift to a power broker from the federal capital.
Apart from South Carolina, next Tuesday's votes will be in another key southern state, Missouri, as well as Arizona and New Mexico in the west and Oklahoma and North Dakota in the mid-west.
And on 7 February there will be caucuses in Michigan and Washington state.
Dean is expected to concentrate on Missouri and Michigan, where he went on Thursday, because it has a higher number of delegates at stake.
He said: "I am going to work like hell and we are going to win."