Sen. Joe Lieberman (I-Conn.) will host a fundraiser for Senate Majority Leader Harry ReidHarry ReidThis obscure Senate rule could let VP Mike Pence fully repeal ObamaCare once and for all Sharron Angle to challenge GOP rep in Nevada Fox's Watters asks Trump whom he would fire: Baldwin, Schumer or Zucker MORE (D-Nev.), whom he has often antagonized, on Sunday in Greenwich, Conn.

Lieberman left the Democratic Party after losing his Senate primary in 2006 and has had a tempestuous relationship with Democrats ever since.

He caucuses with his former party but he campaigned for Republican Sen. John McCainJohn McCainOvernight Defense: General warns State Department cuts would hurt military | Bergdahl lawyers appeal Trump motion | Senators demand action after nude photo scandal Senate lawmakers eye hearing next week for Air Force secretary: report House Intel chairman under fire from all sides MORE (Ariz.) in the 2008 presidential campaign, and many Democrats were unhappy with his criticism of Barack ObamaBarack ObamaSpicer: Trump is 'very confident that he will be vindicated' on surveillance claims Bush DHS secretary: 'Vladimir Putin is winning' Trump ally calls for US to roll back climate commitment MORE.

Reid was under pressure in January 2009 to yank Lieberman’s chairmanship of the Homeland Security Committee, but decided against it.

Lieberman spokeswoman Erika Masonhall said the two men remain close.

"Sen. Lieberman supports his good friend Sen. Reid and was more than happy to help in his reelection efforts," Masonhall said.

From the Connecticut Post:

The gesture of goodwill toward Reid, who was quoted earlier this year as saying that Lieberman double-crossed him on health care reform, has thrown even the most politically astute for a loop.

Connecticut's top Democrat had to go back more than a year -- to a fundraiser coinciding with President Barack Obama's inauguration -- to recall the last time she saw Lieberman at a party event.

"If they're friends, he could be helping a friend. I don't know, though," said Nancy DiNardo, the state Democratic Party chairwoman.

Democrats in the know say this is the second time in about a year that Reid has hit the Greenwich fundraising circuit, taking advantage of the deep pockets of a town elite that doesn't discriminate when it comes to political stripe.

Hosting Reid this time around is venture capitalist Dan Ciporin and his wife, Jill, at their $4 million midcountry home, according to the reception's invitation, which suggests a minimum donation of $1,000 per person. Individuals can donate up to $2,400 for the primary and $2,400 for the general election to Reid, who is seeking a fifth term.