After months of back-and-forth negotiations and overtures from the White House, Sen. Joe Manchin (D-W.Va.) chose an appearance on "Fox News Sunday" to announce he was torpedoing President Biden's signature agenda.

The big picture: The unexpected announcement via the conservative-leaning Sunday morning show just days before Christmas sent fellow Democrats reeling. It infuriated progressives, who'd warned for months of the potential for such an outcome. And it stirred new speculation about the GOP courting a party switch.

• "Sen. Manchin’s comments this morning on Fox are at odds with his discussions this week with the president, with White House staff, and with his own public utterances," White House press secretary Jen Psaki said on Sunday.
• "Weeks ago, Sen. Manchin committed to the president, at his home in Wilmington, to support the Build Back Better framework that the president then subsequently announced. Sen. Manchin pledged repeatedly to negotiate on finalizing that framework 'in good faith,'" she added.
• "If his comments on Fox and written statement indicate an end to that effort, they represent a sudden and inexplicable reversal in his position, and a breach of his commitments to the president and the senator’s colleagues in the House and Senate."

How we got here: Manchin never agreed to support the size and scope of Biden's ambitious Build Back Better spending package and has long sought to bring the price tag to around $1.75 trillion and force more transparency over long-term costs.

• House progressives long held off on passing a separate infrastructure bill because of concerns it was their only leverage over Manchin.
• The question now is, where does this leave Biden and the Democrats' agenda as they head into 2022 midterms that could cost them control of the House and Senate?

Driving the news: Manchin had harsh words for his party, implying the Democrats' agenda is making the country unsafe.

• "My Democratic colleagues in Washington are determined to dramatically reshape our society in a way that leaves our country even more vulnerable to the threats we face. I cannot take that risk," he said in a statement after his Fox appearance.

The intrigue: A source close to Manchin told Axios the White House and leadership were notified of his intentions before his appearance on the show. But sources familiar with the discussions said it was a staffer who reached out — not Manchin himself. The White House got only about a 30-minute heads up.

In a twist of timing that is garnering fresh eyes, Senate Minority Leader Mitch McConnell (R-Ky.) said last week "it would be a great idea" for Manchin to switch to the Republican Party.

• The comment came after McConnell and Manchin had a meeting as negotiations continued for the plan.
• "As you know, he likes to talk," McConnell said of Manchin. "It would not surprise you to know that I've suggested for years it would be a great idea, representing a deep-red state like West Virginia, for him to come over to our side."
• But "I don't think that's going to happen," the GOP leader added.
• Manchin has been asked often in the past whether he's would switch parties but has always reiterated his intention to remain a Democrat.

What they're saying: "For five and a half months, I have worked as diligently as possible meeting with President Biden, Majority Leader Schumer, Speaker Pelosi and my colleagues on every end of the political spectrum to determine the best path forward despite my serious reservations," Manchin said in a statement.

• "I have made my concerns clear through public statements, op-eds and private conversations," he said.
• "I have always said, 'If I can’t go back home and explain it, I can’t vote for it.' Despite my best efforts, I cannot explain the sweeping Build Back Better Act in West Virginia and I cannot vote to move forward on this mammoth piece of legislation."

Pelosi said on Sunday night she is hopeful that an agreement can still be reached, "so that this vital legislation can pass as soon as possible next year."

Go deeper: Manchin tanks Biden’s $1.75 trillion spending plan

Axios' Alayna Treene contributed reporting.

Editor's note: This article has been updated with Speaker Pelosi's comment.