Update (1512ET): Manchin has denied rumors he's thinking of leaving the Democratic party, telling CNN's Manu Raju that it's "bullshit."
Manchin denies story he’s considering leaving Democratic Party: “It’s bullshit,” he told me. He added: “I have no control of rumors.”— Manu Raju (@mkraju) October 20, 2021
MANCHIN to @burgessev and me on the report he is threatening to leave the Democratic Party if his demands are not met on infrastructure: “I can’t control rumors and it’s bullshit, bullshit spelled with a B, U, L, L, capital ‘B’”: pic.twitter.com/ex8iHMIiSs— Frank Thorp V (@frankthorp) October 20, 2021
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Senator Joe Manchin - the moderate Democrat from West Virginia whose insistence on a smaller social infrastructure bill has become a flashpoint within the Democratic party over more than $4.5 trillion in proposed legislation, is considering leaving the Democratic party and has an exit plan to do so, according to Mother Jones' David Corn (of Russiagate-peddling fame).
According to Corn, Manchin has told associates 'in recent days' that he might leave the Democratic party if President Joe Biden and congressional Democrats don't slash their social spending plan from $3.5 trillion to $1.75 trillion - and that if he left, he would declare himself an "American Independent."
He told associates that he has a two-step plan for exiting the party. First, he would send a letter to Sen. Chuck Schumer, the top Senate Democrat, removing himself from the Democratic leadership of the Senate. (He is vice chairman of the Senate Democrats’ policy and communications committee.) Manchin hopes that would send a signal. He would then wait and see if that move had any impact on the negotiations. After about a week, he said, he would change his voter registration from Democrat to independent. -Mother Jones
Manchin - as well as Sen. Kyrsten Sinema (D-AZ) - are two crucial Senate votes needed by Democrats to pass any legislation via reconciliation (a simple majority), due to Democrats' vanishingly slim margin in the chamber. Both moderate Democrats have to sign off on partisan legislation to achieve the required 51 votes (with VP Harris as tie-breaker).
Meanwhile, progressive House Democrats refuse to sign off on the Senate-passed $1.2 trillion infrastructure package unless the $3.5 trillion plan is passed.
According to the report, Manchin told associates that he was ready to initiate his exit plan earlier this week - and floated the idea to Biden, but that he was encouraged by talks with Sen. Bernie Sanders (I-VT) and top Democrats, who he's met with recently. That said, he believes it's likely that he will leave the party by November 2022.
Manchin has repeatedly said that he has a significant philosophical difference with most of his fellow Democrats. He has told reporters that he believes major programs in the Build Back Better bill would move the United States toward an “entitlement mentality” and that he cannot accept that. In a recent meeting with Biden, Manchin told the president that he sees government as a partner with the public not the ultimate provider, according to people who heard the senator’s account of the conversation. He explained to the president that in his view Biden didn’t win the presidency last year by championing progressive proposals, and he pressed the president to recall his campaign promise to bring people together. He also reminded Biden that he has vowed not to support any package unless it contains the Hyde Amendment, which bans the use of federal funds to pay for abortions, except in cases of incest or when the life of the mother is at risk. -Mother Jones
All of that said, we're not sure how much on an impact a Manchin defection would have over negotiations - since he's essentially a Republican in the eyes of his party.