(CLOCKWISE FROM TOP LEFT) Ron Barber (D-Ariz.), Cheri Bustos (D-Ill.), Nick Rahall (D-W. Va.) , Kyrsten Sinema (D-Ariz.). (Reuters, AP, The Washington Post/Reuters, AP, The Washington Post)

The Blue Dogs want to bark again, maybe even bite one day.

Four years ago, they were the most influential voting bloc on Capitol Hill, more than 50 House Democrats pulling their liberal colleagues to a more centrist, fiscally conservative vision on issues such as health care and Wall Street reforms.

Now, the Blue Dog Coalition is a shell of its former self, shrunken to just 15 members because of political defeat, retirements after redrawn districts left them in enemy territory and just plain exhaustion from the constant battle to stay in office. Several are not running for reelection in November, and a few others are top targets of Republicans.

In danger of losing even more clout, the leading Blue Dogs are regrouping and rebuilding. They are adding four members to their ranks this week — Reps. Ron Barber (Ariz.), Cheri Bustos (Ill.), Nick J. Rahall II (W.Va.) and Kyrsten Sinema (Ariz.) — and angling to play a key role in bipartisan talks over the next few years in the belief that the polar tension in the Capitol will thaw.

“We’re in this for the long haul,” Rep. Kurt Schrader (Ore.), co-chairman of the Blue Dogs, said in an interview, predicting that the Democrats could regain the majority only if they are once again competitive in those rural and Southern districts. “We’re the way the Democrats are going to get back into the majority.”

Center Forward, a super PAC, is dedicated to supporting the group’s members in elections, proving effective in 2012 races. In a rare elevation, of one of their own — Joe Donnelly (Ind.) — was elected to the Senate.

The group wants its power to grow and thinks that the tea party influence on House Republicans will begin to wane, leaving many rank-and-file GOP lawmakers searching for Democratic allies to restore the legislative process. “Maybe because of the heightened partisanship in this Congress, you’re seeing more and more members interested in working across the aisle,” Schrader said.

But Republicans aren’t easing up on the Blue Dogs. The four new members come from swing districts that the National Republican Congressional Committee (NRCC) is targeting. Just seven Democrats are left in districts that GOP presidential nominee Mitt Romney won in 2012, and six of them are Blue Dogs .

Early last year, the NRCC created a task force built around winning those districts through locally focused campaigns, rather than just trying to paint the politicians as clones of President Obama or House Minority Leader Nancy Pelosi (Calif.).

The Republicans believe this helped push two longtime Blue Dogs, Reps. Jim Matheson (Utah) and Mike McIntyre (N.C.), to announce they will retire, and they are waiting to see whether others on the “red zone” target list will do so as well.

“This is an end of an era; moderate Democrats are no longer welcome in President Obama’s and Nancy Pelosi’s party. Without McIntyre and Matheson and moderate candidates like them, Democrats have no path to the majority,” said Andrea Bozek, spokeswoman for the NRCC.

In some ways, the coalition is almost back to its founding days in 1995.

After Republicans made historic gains in 1994, routing longtime Southern strongholds that had tilted to the right, a small group of remaining Democrats from rural districts created the Blue Dogs around the principle of fiscal restraint. Slowly but surely, their ranks grew. By 2006, then-Rep. Rahm Emanuel (Ill.) scoured the countryside looking for future Blue Dogs to recruit, leading to a midterm election that vaulted the Democrats and Pelosi into power.

Back then, Blue Dogs kept some interested Democrats out of their coalition. Their internal rules forbid them from becoming more than 20 percent of the full Democratic caucus, because they do not want to water down their centrist views.

In 2009 and 2010, Pelosi spent countless hours negotiating with senior Blue Dogs over the scope of the Affordable Care Act. The group played a key role in eliminating what liberals had considered a key piece of the health-care legislation, a public insurance option, to assure the overall bill’s passage.

The 2010 midterm election took a particularly painful toll on the coalition, with 28 members either losing or retiring, leaving just 25 Blue Dogs at the start of 2011. Those ranks were further diminished in the 2012 election by a redistricting process that was firmly in Republican control in states such as North Carolina.

John Tanner, a former congressman from west Tennessee who co-founded the coalition in 1995, says he is working with normally Republican-leaning interests on Washington’s K Street to deliver a message that they need to support these centrist Democrats because their GOP opponents tilt toward tea party interests that have not been friendly to the business community.

“It’s an opportunity to reach out to a whole new crowd downtown,” Schrader said of the fundraising potential for the four new Blue Dogs.

Now a lobbyist, Tanner said he wants to help the Blue Dogs grow so that they can have a bloc of voters large enough to exploit House Speaker John A. Boehner’s problems with his right flank. That way, if Boehner (Ohio) loses 25 Republicans on a bill, there would be enough Blue Dogs to lend him support if the legislation were tilted more in their direction.

“The Blue Dogs could play a critical role if they could get a critical mass,” Tanner said.