It’s hard enough for a House Member to stay on Capitol Hill as a lame duck for several months after losing a bruising primary.

It’s even more humbling when the Member must work next to the opponent who defeated him or her.

Four Member-vs.-Member primaries have already been decided this cycle, and bitterness still lingers among several of those lawmakers.

From now through Election Day, 18 more Members will run against each other thanks to redistricting, which created more of the unique matchups than usual this cycle.

“There are no Member-on-Member primaries that are pretty,” said Rep. Steven LaTourette (R-Ohio), who hails from a state where four Members ended up squaring off against a fellow lawmaker.

The closer the Members were before the contest, the harder to mend the relationship and move on. One-time allies no longer speak or are reduced to merely exchanging pleasantries.

Rep. Dennis Kucinich declared himself the “president” of Rep. Marcy Kaptur’s “fan club” several years before the Ohio Democrats ran against each other in a March primary. Kaptur defeated Kucinich by a substantial margin, and the two haven’t talked since.

“I haven’t spoken to her,” Kucinich told Roll Call last week. “We haven’t talked.”

“I hardly see him,” Kaptur said a few moments later. “I think he’s probably reevaluating many things.”

Similarly, Reps. Bill Pascrell and Steven Rothman dined together at the National Democratic Club ever since they came to Congress in 1996. The two Democrats even sang karaoke on occasion.

But Pascrell and Rothman have made only small talk since their nasty June primary in New Jersey’s 9th district.

“We haven’t sat down to eat yet,” Pascrell, the victor, said. “But we’ve exchanged pleasantries, and that’s where it’s at. Relationships change. Many times relationships are personal.”

In the six weeks since the primary, Rothman has rarely ventured to the corner of the House floor where members of the Pennsylvania and New Jersey delegations convene, sources said. One aide bluntly summed up their relationship status as “fine.”

After the primary, Pascrell blamed Rothman for running a negative race. Pascrell and his allies also saw the primary as unnecessary because Rothman could have run against a Republican incumbent in another district, although most of the redrawn 9th district included Rothman’s current territory.

Rothman’s spokesman did not return a request for comment last week.

“Maybe the relationship will get back to where it was, and maybe it won’t,” Pascrell said.

So far, these matchups show it’s easier for Members if the two foes aren’t close to begin with.

That was the case in Member-vs.-Member primaries in Illinois and Pennsylvania.

Illinois Republican Reps. Don Manzullo and Adam Kinzinger served in Congress together for less than six months before it was obvious they would challenge each other.

Kinzinger defeated a Democrat in a competitive district in 2010, and Manzullo had not faced a tough race in decades.

It showed. Manzullo took Kinzinger’s attacks personally. He accused the freshman of making his “wife weep” with his direct-mail attacks. Manzullo also called for House Majority Leader Eric Cantor (R-Va.) to step down for supporting Kinzinger.

Four months after Kinzinger’s victory, Manzullo has made amends with his  colleagues, although he has not yet publicly endorsed Kinzinger.

Still, for a Member nicknamed “Mad Dog,” several Illinois Republicans remarked that Manzullo has been particularly cooperative.

“There’s a lot of opportunities for him to go off the rails, and he hasn’t chosen to do it,” one Illinois GOP aide said. “He’s even more of a team player now than he was.”

In particular, Manzullo has worked with freshman Rep. Bobby Schilling (R-Ill.) on a few initiatives in Rockford, Ill., such as transitioning the state-run Thomson Correctional Center to a federal prison. Rockford anchors Manzullo’s current district, but Democrats moved half of the manufacturing hub into Schilling’s district under the redrawn map.

As in the Illinois race, Democratic Reps. Jason Altmire and Mark Critz didn’t know each other well before their April primary in southwestern Pennsylvania’s 12th district. Critz, a longtime district director for the late Rep. John Murtha (D-Pa.), won a special election in May 2010. The two Democrats met only a handful of times before Critz’s victory, and both Democrats have since run in different Congressional social circles.

After Altmire lost the divisive primary by a couple of points, he immediately offered Critz his endorsement in his concession call. Democrats said he’s been helpful ever since.

“Mark is grateful for the advice and support Congressman Altmire has provided,” said Mike Mikus, a Critz campaign adviser.

Altmire declined to comment. But he has been so helpful that at least one Democrat publicly questioned his motives. Critz faces a tough race this November, and if he loses, Altmire would be the heir apparent to run in 2014.

“Altmire is helping,” said Jack Hanna, chairman of the Pennsylvania Democratic Party’s Southwest Caucus. “He’s being nice to people, so maybe he’s pocketing something to pull back out in the future.”

Of course, it’s in the losing Members’ interests to make amends with their colleagues. That’s especially true if the defeated is angling for a K Street career or future campaign.

Either way, these Members have months to mull their next career move — and legacy — before they cast their final vote.