WASHINGTON Democrats believed they had an agreement to extend monthly child tax credit payments for another year until Sen. Joe Manchin (W.Va.) expressed fresh concerns about the proposal this week.

I was stunned by that, Senate Majority Whip Dick Durbin (Ill.), the chief Democratic vote-counter, said Thursday when asked about Manchins position on the issue.

That is such a critical element, the largest tax cut for working Americans in the history of the United States ... for this to come up as an issue toward the end was stunning, he added.

Sen. Michael Bennet (Colo.) said he was very, very surprised because he thought there was a deal to extend the program for one year.

Manchin had previously sought to exclude lower- and higher-income households from receiving the monthly benefit, but after weeks of negotiations with both Manchin and Sen. Kyrsten Sinema (D-Ariz.), the White House announced in late October a Build Back Better framework that included the child benefit through 2022. Democrats rejoiced that Manchins work requirement was dead.

But on Wednesday, Manchin would only say hes always supported the child tax credit, a tax policy that has existed for decades, while pointedly declining to tell HuffPost whether he supports the specific version Democrats are trying to extend with monthly payments and full benefits even for people with no earned income.

Manchin later said on Wednesday he wanted Democrats to extend the child tax credit for 10 years instead of just one. Doing so would blow up the rest of the $1.75 trillion bill, since a decade of child tax credit payments would cost more than $1 trillion all by itself.

Ongoing talks between Manchin and President Joe Biden over the legislation are said to be going poorly , with sharp disagreements over the child tax credit and other provisions. Without all 50 Democrats on board, the bill is effectively stalled and a vote isnt likely until January at the earliest.

Were frustrated and disappointed, Durbin added on Thursday. We had more than ample opportunity to reach ... a Democratic agreement. I never assumed any bipartisan support. We missed an opportunity, but Im not giving up.

The sliver of good news for Democrats is that Manchin hasnt formally declared his opposition to the bill, which is projected to cost $1.7 trillion over 10 years. The fact that hes continuing to negotiate suggests there may yet be a window for a deal.

HuffPost readers: Have you come to rely on monthly child tax credit payments? Tell us about it email arthur@huffpost.com . Please include your phone number if youre willing to be interviewed.

Its possible that Congress reaches some sort of agreement on a stand-alone extension of the child tax credit payments, which will cease this week if lawmakers do not act. Sen. Ron Wyden (D-Ore.) asked the Senate for unanimous consent Wednesday to add a child credit extension to an unrelated bill, but Republicans said no.

Sen. Cory Booker (D-N.J.), a leading advocate of the benefit, told HuffPost Democrats were talking about a stand-alone extension a lot.

People are bouncing that idea around, Booker said Thursday morning. If anything comes of it or not, were gonna see. Todays gonna be, I think, a very eventful day.