House Democrats are struggling to come up with enough votes to pass a critical measure to lift federal spending caps.

Leaders hoped to bring up the measure this week and pass it ahead of a two-week recess. But now it’s not certain enough Democrats will support the measure because of mounting opposition from the progressive wing, who want more money for domestic budgets.

“The whip team is not very sure of where we are,” Budget Committee Chairman John Yarmuth, D-Ky., said after a closed-door meeting with Democratic lawmakers in the basement of the Capitol Tuesday morning.

The budget has proven to be a difficult issue for Democrats.

Yarmuth has largely abandoned an effort to pass a budget resolution that would provide a long-term spending plan for the party because members of the caucus cannot agree on spending levels.

Yarmuth’s budget panel advanced by a narrow margin last week a bill that would lift the current domestic spending limit by 5.7%, to $631 billion in fiscal 2020, and to $646 billion in fiscal 2021. The measure would raise defense spending by 2.6% over the current cap — to $664 billion, in 2020. Defense spending would be capped at $680 billion in fiscal 2021.

Three progressive Democrats on the panel voted “no,” in a warning to the party leadership that floor passage could run into obstruction by the progressive wing.

Among the Budget panel "no" votes was Rep. Pramila Jayapal, D-Wash., who wants to increase domestic spending and decrease defense spending.

Jayapal introduced an amendment in the House Rules Committee to make defense and non-defense spending equal in fiscal 2020 and 2021, which would boost domestic spending by $33 billion. The money could be used to invest in critical infrastructure projects and other needs outside of the military, Jayapal said.

“Here’s a real opportunity to tell people we are investing in their future,” Jayapal said after Tuesday’s meeting with the caucus. “We are giving money to a Pentagon that is increasingly wasteful, hasn’t conducted an audit. We have got to start addressing this.”

Democratic leaders, including Yarmuth, took a more pragmatic stance and said the proposed caps align realistically with what can clear Congress and earn the president’s signature.

President Trump’s proposed 2020 budget provides an overall $750 billion in military spending while keeping domestic spending at the caps level of $542 billion.

The Senate has not yet agreed on spending caps, but Republicans are in the majority and would not likely agree to Jayapal’s proposed increase in domestic spending.

“If we are going to get an agreement, we need to get an agreement between the House, the Senate, and the president,” Majority Leader Steny Hoyer, D-Md., said Tuesday. “That’s the reality.”

House Republicans have signaled they will oppose the measure, which means in order for it to pass, Democrats must mostly stick together. They can only lose 17 votes.

As of Tuesday, passage appeared difficult to achieve this week in part because Democrats intend to leave early to attend an annual planning retreat.

“I certainly am frustrated by the lack of equity between defense and non-defense spending,” Rep. Judy Chu, D-Calif., told the Washington Examiner. “I do think we have to weigh the necessity of having an actual bill versus one that could not pass. I do want to see a bill pass that actually has non-defense spending increased.”