The congressional candidates former President Clinton is supporting in 2012 have something in common: They all backed his wife’s presidential bid four years ago.

Sources close to Clinton said he wants to help those who put themselves on the line to support the former first lady’s campaign for the White House. But with Hillary ClintonHillary Diane Rodham ClintonGOP rushes to cut ties to Moore Papadopoulos was in regular contact with Stephen Miller, helped edit Trump speech: report Bannon jokes Clinton got her ‘ass kicked’ in 2016 election MORE serving in the Obama administration and Chelsea Clinton working for NBC News, Bill ClintonBill ClintonTop Oversight Dem pushes back on Uranium One probe Bill Clinton hits Trump, tax reform plan in Georgetown speech The Hill's 12:30 Report MORE is the only member of the family in a position to hit the campaign trail.

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Clinton announced on Tuesday that he will travel to Texas in April to endorse Rep. Silvestre Reyes (D-Texas), who faces serious primary opposition. Reyes not only endorsed Hillary Clinton in 2008, he served as her campaign co-chairman in charge of the Southwest region.

Earlier this month Clinton picked sides in an intraparty fight when he backed Rep. Mark Critz (D-Pa.) over Rep. Jason Altmire (D-Pa.). Altmire didn’t endorse in the 2008 primary, but Critz was a top staffer for former Rep. John Murtha (D-Pa.), a stalwart Clinton ally. Critz, who is squaring off with Altmire in a redistricting-induced primary on April 24, has aired television ads in Pennsylvania promoting the endorsement from the popular former president.

Clinton’s move to endorse in the Altmire-Critz race prompted speculation about what he might do in another Democratic primary — this one in New Jersey, where Democratic Reps. Bill Pascrell and Steve Rothman are battling it out ahead of a June primary.

The loyalties from 2008 were clear: Pascrell backed Hillary Clinton; Rothman backed then-Sen. Barack ObamaBarack Hussein ObamaOvernight Cybersecurity: What we learned from Carter Page's House Intel testimony | House to mark up foreign intel reform law | FBI can't access Texas shooter's phone | Sessions to testify at hearing amid Russia scrutiny Russian social media is the modern-day Trojan horse Trump records robo-call for Gillespie: He'll help 'make America great again' MORE (D-Ill.).

Pascrell declined to say whether he had sought Clinton’s nod, saying the ground game would be much more important to determining the race’s winner.

“I’d love to have the endorsement of the president. I’d love to have the endorsement of Bill Clinton,” Pascrell told The Hill. “But it doesn’t tell us where the campaign is. I’m not going to depend on that.”

In March, Clinton waded into a hotly contested Democratic primary in Maryland, backing businessman John Delaney over state Sen. Rob Garagiola (D). Clinton called Delaney, who later won the primary, a lifelong Democrat who knew how to create jobs. But Delaney, a major Democratic donor, also reportedly raised more than $800,000 for then-Sen. Hillary Rodham Clinton (D-N.Y.) in 2008.

In another primary pitting two incumbent Democrats against each other, Clinton has backed Rep. Brad Sherman (D-Calif.), who will face Rep. Howard Berman (D-Calif.) in a June primary. Sherman, who endorsed Hillary Clinton in the 2008 presidential race, has a photo of himself with former President Clinton featured prominently on the front page of his campaign website. Berman endorsed Obama.

“Brad has worked tirelessly for the people of California and I hope he will continue to do so,” reads a note from Clinton on Sherman’s website.

The Clintons have long been known for their loyalty to supporters.  In 2010, the former president also campaigned for family loyalists, such as former Rep. Kendrick Meek (D-Fla.), who was in a tough Senate race, and Rep. Heath Shuler (D-N.C.), both of whom endorsed Hillary Clinton in 2008.

And, in what was seen as a Bill Clinton/President Obama face-off last cycle, the former president backed Andrew Romanoff in Colorado’s Democratic Senate primary while Obama backed Michael BennetMichael Farrand BennetBipartisan lawmakers can rebuild trust by passing infusion therapy bill GAO to investigate Trump's voter fraud commission 2 election integrity commission members protest lack of transparency MORE, who went on to win the seat. Clinton, however, did campaign for Bennet in the general election.

Clinton insiders, who requested anonymity to be able to speak candidly, said Clinton is willingly carrying the burden of repaying those who worked for his wife four years ago. But there are more requests coming in than the former president’s schedule can accommodate.

It’s no surprise that Democrats, leery of getting too close to Obama and eager to remind voters of more prosperous years under a Democratic president, are seeking out the good graces of Clinton, whose approval ratings have surged since he left the White House in 2001.

“He’s very popular, he makes the case for a constructive role for the public sector and he’s a good fundraiser,” said Rep. Barney Frank (D-Mass.), who is not seeking reelection. “He’s as good an endorsement as you get.”

— Last updated at 8:25 p.m.