Originally Published: 13 DEC 21 08:04 ET

Updated: 13 DEC 21 09:31 ET

By Kaitlan Collins and Kate Sullivan, CNN

(CNN) -- President Joe Biden will speak with Sen. Joe Manchin on Monday as the President works to secure the West Virginia Democrat's support for his expansive economic and climate bill he wants passed by the end of the year.

The President "looks forward to speaking directly" with Manchin to make his case for why the legislation should move forward, White House press secretary Jen Psaki told reporters at a White House briefing. Psaki said the two would speak Monday afternoon.

The conversation comes as Manchin continues to voice serious concerns he has about the size and scope of the centerpiece of Biden's domestic agenda. Manchin's vote is key to the legislation's passage, and Biden has publicly expressed uncertainty about whether he can get Manchin's support.

Psaki said Monday the President believes his conversations with Manchin have "always operated in good faith, and he expects this to follow that same approach." She noted Manchin has been in close touch with senior White House staff members over the past several weeks.

Biden spoke with Manchin late last week, according to a source familiar with the conversation. During their conversation, Biden made clear to Manchin what is an obvious reality: he needs the senator's vote on this bill. But Manchin conveyed to the President that he was not there yet and expressed deep concerns about the size and scope of the legislation, according to the source.

Earlier on Monday, Manchin spoke to reporters and pointed to high inflation and the bill's reliance on temporary programs as two major reasons why he hasn't backed the legislation.

In a key warning sign, Manchin told CNN the bill shouldn't rely on temporary spending that will likely become permanent.

"I don't think that's a fair evaluation of saying we are going to spend X amount of dollars but then we are going to have to depend on coming back and finding more money. ... I'm concerned about paying down debt too," Manchin said.

The senator said the bill should be "within the limits" of "what we can afford," and said the temporary programs in the bill should be extended for 10 years to be "transparent" about how much the bill actually costs.

Manchin said inflation is a real concern still after last week's report showing inflation spiking in November to a 39-year high.

The moderate Democrat also said the Congressional Budget Office report that Republicans requested showing the deficit would increase by $3 trillion over the next decade was "very sobering" and said he's been "very concerned" about the price tag. But Manchin said he wants to hear the President's view when they speak by phone later on Monday.

The latest CBO score is a Republican-led effort to show that the bill costs more than Democrats say it does, but Democrats are arguing that many provisions in their proposal sunset and therefore the true cost is not what Republicans say it is.

Manchin's support for the bill -- a $1.9 trillion spending plan focused on expanding the nation's social safety net, reducing Americans' child care and health care costs, and climate change -- is key to moving Democrats closer to getting the legislation to Biden's desk and signed into law.

But Manchin has publicly raised a number of concerns about the legislation, which passed the Democrat-controlled House last month. The senator is seeking to pare down the bill in several areas, including paid family leave, a methane fee on emissions from energy producers and a Medicare expansion to cover hearing costs. He is also seeking changes to some of the provisions in the tax portion of the bill.

The President said Friday he doesn't know if he can get Manchin on board to support the bill but that he would be speaking to the senator this week. He reiterated his argument that the plan "doesn't raise inflation" and pointed to global supply chain issues as the cause for the increase in consumer prices that are frustrating Americans.

White House press secretary Jen Psaki told reporters on Friday that when Biden and Manchin speak this week she expects the President to make the case "that this is exactly the time to pass this bill and move it forward so that we can lower costs for the American people on all of those topics, including insulin, and areas that really force American families to pinch pennies."

Senate Majority Leader Chuck Schumer said last week the Senate was on track to bring the legislation to the floor before Christmas, but getting the bill done in that timeline remains a heavy lift because of procedures of the Senate and lingering differences among Democrats.

Democratic Sen. Amy Klobuchar of Minnesota told CNN's Jake Tapper on Sunday that Democrats are going to do "everything to get" the Build Back Better Act done by Christmas. The senator said she was optimistic that Manchin would eventually support the legislation and pointed to his support for bringing down prescription drug prices, which is addressed in the bill.

This story has been updated with additional information.