The ad tugs at the heartstrings, with an elderly man leaning on a cane, talking about being homeless in the wake of a recent storm in Louisiana. Later, the camera pans over to a shot of a man with rolled-up sleeves, talking with office workers around a conference table. This, says the once homeless man, is the guy who “saved” him.

Casual viewers seeing the ad flash across their screens during the 2006 election cycle might be forgiven for thinking it was a solemn, disaster-themed spot for an insurance company. It was, in fact, a pitch for Louisiana voters to re-elect Rep. Charlie Melancon — though the only thing identifying it as such was the fine-print disclaimer at the end, saying that the ad was paid for by the Charlie Melancon Campaign Committee.

Soft-sell appeals of this sort are essential for candidates such as Melancon — the cohort of 63 Democratic House members and eight Republicans who were in districts that had supported the opposition party’s presidential candidate in 2004. These lawmakers account for almost one-sixth of the House, and they fuel a comfortably booming cottage industry for consultants, pollsters and ad wizards who specialize in winning these so-called purple seats.

Democrat Melancon, for example, represents a district south and west of New Orleans that George W. Bush carried in 2004 with 58 percent of the vote. Melancon paid out a cool $1.5 million two years ago to Fletcher Rowley Chao Riddle, the ad consultancy that produced the spots depicting him as a fighter for the interests of plain folks. His campaign spent an additional $95,000 for polling from the firm Anzalone Liszt Research, which has likewise built a specialty in advising candidates in Bush-Democratic districts.

This new breed of campaign consultants typically hews to sotto voce campaign themes: guarded, post-ideological messages that are calculated to reassure cross-party and independent voters.

“I think the common theme in all these successful campaigns is that the candidates carved out their own real estate as independent-minded Democrats,” said Fletcher-Rowley partner John Rowley. His firm counts seven incumbent Democratic clients from purple districts, in addition to Melancon.

Generally speaking, the number of seats that cut against voter preferences in presidential contests has been in long-term decline, thanks both to gerrymandering of incumbent districts and to increased fundraising in congressional races. The shrinking allotment of competitive seats has become much more vital for each party to win or defend.

After the Democrats successfully captured control of the House in 2006, purple seats formed a critical bloc in the majority, one that party leaders want to expand this November as they also aim to win the White House.

Still, Democrats have to campaign in purple districts ever so softly. A key element of the strategy to hang on to these “majority maker” districts is to downplay any suggestion that the incumbents — mostly members of the fiscally conservative Blue Dog Coalition — might rub their constituents the wrong way, ideologically speaking, and to highlight the ways they’ll be fighting on behalf of their districts in more crucial everyday struggles.

With a margin of 569 votes, Melancon won the 2004 election to succeed Republican Billy Tauzin, who had retired to lobby for the pharmaceutical industry. Melancon, like Tauzin, leans conservative on many social and fiscal issues, and he reminds voters that he is his own man — and the go-to guy in times of trouble.

Democrats recently took their carefully tailored message on a successful trial run, scoring wins in two purple-district House special elections in the South earlier this year. Travis W. Childers picked up the northeast Mississippi seat vacated by Republican Roger Wicker when he was appointed to serve out Trent Lott’s term in the Senate. And Don Cazayoux narrowly won Richard H. Baker’s Baton Rouge seat after the Republican retired to work as a hedge fund lobbyist. Both Democrats are social conservatives, favoring gun ownership and school prayer and opposing abortion.

“I’m pro-life and pro-gun,” Childers said in one ad. “I approved this message because I’ll do in Congress what I’ve done in Mississippi — work with both parties, balance budgets and create jobs.”

While downplaying their partisan bona fides, Democratic candidates holding purple seats favor broad testaments to the strength of their personalities and subtle evocations of cultural preferences — perhaps standing in front of a red barn or a green tractor, with a twangy guitar playing in the background — that place them squarely in the mainstream of their constituencies.

“There isn’t any magic sprinkle dust,” said John Anzalone of Anzalone Liszt, which worked on the Cazayoux and Childers campaigns. “We didn’t bash Bush. It’s not a meat cleaver. It’s much more, ‘Hey, I’m the guy who’s going to take care of your needs. I’m going to work in a bipartisan fashion.’ ”

This soft-focus marketing has given fits to Rep. Tom Cole of Oklahoma, chairman of the National Republican Congressional Committee. Cole argues that such candidates aren’t really running as Democrats by supporting gun rights and opposing abortion. Rather than embrace these candidates in the culture wars, Republicans aim to lash them to liberal positions of House Speaker Nancy Pelosi of California and Obama.

“They have to disguise what they are to be formidable candidates,” Cole said. “If they voted up here the way they’re running, believe me, they could all get in the Republican Study Committee and be in good standing.”

So far, the camouflaging strategy works. “In most congressional districts, people want somebody who will relentlessly, if not irrationally, fight for their interests above all others,” Rowley said.

That message can play more powerfully with broad emotional themes, consultants say, as opposed to the drier minutiae of policy debate. In the 2006 cycle, Larry Kissell, a Democrat who narrowly lost his bid to unseat incumbent GOP Rep. Robin Hayes in North Carolina, produced an online ad that featured a country music theme song with the refrain, “I’m takin’ my country back,” while downplaying mention of his party affiliation. Kissell is vying for the seat again this year.

“When it comes to advertising and connecting candidates to the electorate, it’s an emotional connection,” Rowley said. “It’s not always a logical or intellectual connection.”

Candidates in purple districts can further blur their policy profiles by advertising their anxieties about the amoral drift of popular culture, these advisers say — an issue that resonates strongly with conservative-leaning and family-minded voters, but that produces little in the way of sharply delineated policy.

Alan M. Secrest, of polling firm Cooper & Secrest Associates, said candidates benefit from sharing cultural concerns, whether about the Internet or television or the violent video game “Grand Theft Auto.”

“For many of these candidates, they took some time to explain their understanding of popular culture and how popular culture influences children,” said Secrest, whose firm is working with six lawmakers from purple districts in this cycle. “They’re willing to give voice to something that everyone agrees with — liberals, conservatives, Democrats, Republicans.”

The same declarations of independence occur where Republicans are running in districts that Democratic presidential nominee John Kerry carried in 2004.

“I’ve gone against the president and the Republican leadership when I think they’re wrong,” said Christopher Shays of Connecticut, the only remaining House Republican from New England, in an ad citing his support for stem cell research that Bush vetoed. “I believe we are Americans first, and Republicans and Democrats second.”

But as the Childers and Cazayoux elections showed, Democrats are increasingly going the extra mile to embrace stands on social issues that have traditionally been identified with the GOP. In 2006, for instance, Democrat Zack Space wrested control of a Republican seat in Ohio by highlighting a tough stand against amnesty for illegal immigrants — and this cycle he’s trumpeting his recent endorsement from the National Rifle Association.

“When the Republican playbook on Page One is to link every Democrat to the most liberal ideas and politicians they can think of, you’ve got to make the case that this is standard Republican bunk,” Rowley said. “It’s hard to say somebody’s a wacky, out-of-touch liberal if they’ve got the NRA endorsement.”

Florida Democratic Rep. Tim Mahoney, who won GOP Rep. Mark Foley’s seat in 2006 after Foley resigned over a scandal involving sexually inappropriate computer messages to former House pages, argues that the new breed of purple consultants is helping win back so-called Reagan Democrats.

“These guys are bringing them back to the Democratic Party,” said Mahoney, who has already spent $220,000 on Fletcher-Rowley-produced ads this cycle and who lent his chief of staff, Charles Halloran, to work on Childers’ campaign. “It’s hard enough in a bad economy. People don’t want to hear about gay marriage and things like that.”

Rep. Thomas M. Davis III, the Virginia Republican who used to lead the NRCC and is retiring from Congress this year, said Democrats could lose their grip on the purple end of their coalition if they win the White House this year. In the meantime though, Davis says Democrats have shown a flexibility on cultural issues that his GOP colleagues would do well to emulate.

“The Democrats have cracked the code, and we still have an admissions test to get into the party and be a candidate,” said Davis, noting that his party has suffered a 10- to 12-point slide in voter approval ratings since 2000 over big-ticket issues such as Iraq and the economy. “Democrats are smart. They want to win. Our guys still want to be right.”

Policing the impression of excessive partisanship does complicate the essential business of raising campaign cash in purple elections, however. Mike Fraioli, whose firm Fraioli and Associates raises money for Democrats, says he has found it helpful to vet fundraising sources in some races — even though such donations tend to be “vanilla,” he says, “not hard right or hard left.” Too much money from the wrong kind of contributor can skew an intended message of sunny bipartisanship, Fraioli says, so he gives candidates a questionnaire to sort out whether they would decline money from pharmaceutical or tobacco interests, for example.

“A candidate needs to decide who they are, what they’re about, why they’re running,” Fraioli said.

Indeed, for all the painstaking strategy, some purple consultants still say the most vital political ingredient is the candidate. “Travis Childers had an amazing gut,” Anzalone said. “He overruled us multiple times because of his gut. He was right every time.”

FOR FURTHER READING: Democrats’ centrist congressional agenda, CQ Weekly, p. 1520; Childers victory, p. 1363; Cazayoux victory, p. 1268; 2008 congressional campaign outlook, p. 1086.