It’s been a very tough cycle for Blue Dog Democrats, but Tuesday took the cake.

Rep. Tim Holden (D-Pa.) on Tuesday became the latest Blue Dog Democrat to lose his seat in Congress. And he’s got plenty of company. (Dave Mckeown, AP)

The cumulative effect: For a caucus that featured 54 members last Congress and saw that number sliced to 26 after the 2010 election, the number could be halved again if things go really poorly this November.

Already, five of 25 current Blue Dogs have announced their retirements (former congresswoman Gabrielle Giffords, who had been No. 26, resigned as she recovers from an assassination attempt), two have now lost primaries, and another eight are legitimately vulnerable in the 2012 election — in large part because redistricting affects them in a very disproportionate way.

In other words, only about 10 Blue Dogs are sure-things to return next Congress, and the caucus needs new blood.

And yet, there are few prospects for an infusion of moderate and conservative Democrats to replenish the wilting Blue Dog caucus. And absent a concerted effort to keep the caucus alive — including by non-Blue Dog Democrats — we’re not likely to see it ever return to anywhere near its 2010 power.

Compared to the 2006 and 2008 cycles, when the Democratic Congressional Campaign Committee sought a cadre of Blue Dog Democrats to re-take the House, there aren’t nearly as many self-identified Blue Dogs set to run this time around. And that fact is causing some consternation.

An aide close to the Blue Dogs told The Fix that the group “is not happy with DCCC’s progress in recruiting moderates.” Added the aide: “The recruiting that we’ve done, we’ve done ourselves.”

The aide did say that the committee is starting to come around and recruit more moderates, but it’s also very late in the recruiting season right now, with filing deadlines passed in many states.

Added another Blue Dog sympathizer: “The Democratic Party on all sides needs to realize that if they don’t hold moderates, they don’t hold these seats. … You have our people on the left, labor, and they pull stunts like this in Pennsylvania, the party will have a great time having meetings in the Rayburn Room outside the Speakers office for a long time.”

(Labor helped Rep. Mark Critz defeat Altmire in a district that went 54 percent for John McCain in 2008 — in other words, a seat where Democrats might previously have wanted a Blue Dog Democrat like Altmire as their nominee.)

To this point, the Blue Dog PAC has endorsed eight candidates: Leonard Bembry (FL-02), Clark Hall (AR-01), former congressman Nick Lampson (TX-14), Brendan Mullen (IN-02), Hayden Rogers (NC-11), Ted Vick (SC-07), Rob Wallace (OK-02) and former congressman Charlie Wilson (OH-06).

Most of the endorsees, though, are running in tough districts for Democrats to win. Many of these districts have long been conservative, became moreso after redistricting, and have begun to embrace Republicans. And it’s a lot harder to win a seat as a conservative Democrat challenger than to hold one as an incumbent.

Blue Dog Caucus co-chairman John Barrow (D-Ga.) said that without redistricting reform, its going to be very hard for the caucus to return to its 2010 ranks.

“The field of prospects and candidates is a rich and fertile field, but it’s a very hostile and sterile environment for them to run in,” Barrow said. “The districts they have to run in have been rigged, and that moderate majority has been suppressed.”

Democrats insist that they are making a good faith effort to keep the caucus alive (Blue Dog Rep. Jim Matheson of Utah is on the DCCC’s recruitment committee, for example), but they note that the Republican takeover of the South has strained the caucus and reduced the pool of talent available. And many moderate Democrats that are running elsewhere in the country may not fit the same socially conservative mold that Blue Dogs are known for.

Instead of going the Blue Dog route, they note, some of the candidates have chosen to align themselves instead with another moderate group — the more socially liberal and fiscally conservative New Democrat Coalition, which DCCC Chairman Steve Israel once belonged to. (Israel is also a former Blue Dog, for what it’s worth.)

The New Democrats, in contrast to the Blue Dogs, currently boast more than 40 members and have endorsed 20 candidates this cycle.

Many of these members are running outside the South and may not be comfortable aligning with socially conservative Democrats; the New Democrat Coalition is a great way to claim the “moderate” label without risking being called a “conservative Democrat” and risking the wrath of the donor base (or even a primary challenge).

Democrats say, in addition to the Blue Dog candidate named above, that they still have many moderate candidates who may or may not embrace the Blue Dog label — many of them running in districts formerly held by Blue Dogs. These include: Q. Byrum Hurst (AR-04), Sal Pace (CO-03), Pam Gulleson (ND-AL), Eric Stewart (TN-04), Dave Crooks (IN-08), Brad Harriman (IL-12) and Gary McDowell (MI-01).

McDowell, though, didn’t embrace the label in 2010 despite running in a district long-held by Blue Dog Bart Stupak (D-Mich.).

Pace, like McDowell, is running a district formerly held by a Blue Dog. A spokesman said the campaign is working with the Blue Dog PAC on an endorsement, but that it is not using the label during its campaign.

“We’re not into labels,” the spokesman, Chad Obermiller said. “But yeah, we’ve reached out to them. For our race, it’s about people not politics.”

Other candidates didn’t respond to requests for comment about whether they identify with the Blue Dog label.

That hesitance to embrace the label of “conservative Democrat” seems to be a natural progression for our body politic today, in which it’s simply very hard to build a political career by fusing those two words together. Combine that with the GOP’s almost-complete takeover of the South, and it’s not surprising that the ranks of Blue Dogs continue to decline.

And we wouldn’t expect their ranks to ever again approach the 50-plus members they had last cycle.