If Sen. Joe Manchin bolts the Democratic Party, he'd be more likely to switch to independent — and caucus with the Democrats — than become a Republican, people close to him tell Axios.

Driving the news: Manchin’s surprise body blow to President Biden’s Build Back Better agenda set off new speculation across the Democratic Party — including inside the White House — that he may leave the party next year.

• The timing and destination of Manchin's declaration: "I can’t get there. This is a no" — on "Fox News Sunday," days before Christmas — seemed designed for maximum impact. But it wasn't immediately clear to what end, or what had prompted it.
• The White House was caught off guard and responded with an angry statement.
• Manchin has consistently denied any interest in leaving the party, most recently after Mother Jones reported in October that Manchin had told associates that he had an exit plan. "I can’t control rumors, and it’s bull**** ... capital B," Manchin told reporters.

Why it matters: A formal defection by Manchin could make passing parts of Biden’s $1.75 trillion plan all the more difficult for Democrats.

• But it would also bring clarity to Biden’s political predicament: With 50 votes, his party formally controls the Senate. In reality, any single Democrat can take the party hostage on any given issue.
• Yes, Democrats control the floor schedule and can muscle through judges and ambassadors, but only with a fair amount of procedural pain.
• As long as Democrats pursue big legislative changes through reconciliation, they face big risks from any single member.
• Sen. Kyrsten Sinema (D-Ariz.) effectively rewrote the Democrat's tax provisions — and killed a top line corporate rate hike — to offset their spending plans.

The big picture: Progressives were worried all year that they would whittle down their spending ambitions to bring Manchin aboard, only to have him pull the rug out once the negotiations got real.

• They knew that their only leverage was holding up the $1.2 trillion infrastructure package, and they were right. As soon President Biden signed the infrastructure bill into law, they lost all leverage and Manchin was in the driver's seat — though it's not clear they could have brought Manchin along even if they'd held out longer.
• Progressives told Axios’ Alexi McCammond they want Biden to fight back against Manchin aggressively — an instinct reflected in White House press secretary Jen Psaki's statement.
• Some want the president and progressives including Sen. Bernie Sanders to travel to West Virginia to meet directly with Manchin’s constituents and champion the benefits of lower prescription drug costs, universal pre-K and other child and health benefits the legislation could have in the state.
• "I would take this as a call to arms,” said Joseph Geevarghese, executive director of Our Revolution, a Sanders aligned group. "This is Manchin saying, 'I'm going to play hardball until the very end.'"

Anger at Manchin coursed throughout the party Sunday and some Democrats with races next year pivoted from attacking GOP rivals to going after Manchin.

• Rep. Val Demings (D-Fla.), seeking to unseat Sen. Marco Rubio, told supporters in an email that there’s an urgency to expand the party’s majority because “we can’t let any one senator stand in the way of progress like the Build Back Better Act… will you support my campaign to become the 50th vote Democrats need in the Senate … ?”

Between the lines: Many Democrats told Axios on Sunday that they don’t believe Build Back Better is truly dead and that it’s a matter of figuring out what can actually pass in 2022.

• Lawmakers, leadership aides and outside strategists told Axios’ Sarah Mucha and Andrew Solender they believe the likely path is one touted by Rep. Suzan DelBene (D-Wash.), the chair of the House’s 97-member centrist New Democrat Coalition, who is proposing regrouping around a refined proposal with fewer programs that last a longer duration of time.
• Rep. Josh Gottheimer (D-N.J.) tweeted he would “do my part to help bring everyone back to the table." Rep. Abigail Spanberger (D-Va.) said in a statement it is “unacceptable” for Manchin to abandon “productive” talks.
• House Speaker Nancy Pelosi wrote in a "Dear Colleague" letter Sunday night: "While it is disappointing that we may not have a law by the end of the year, we are hopeful that we will soon reach agreement so that this vital legislation can pass as soon as possible next year."

Be smart: No one knows if Manchin can be convinced to support a pared-down version of Build Back Better, not even the White House.