WATCH: Jen Psaki holds White House news briefing

The White House said President Joe Biden knows getting his agenda through Congress “is hard” but he is determined to work with Democratic leadership to win the votes.

Watch in the player above.

Democratic leaders are trimming back Biden’s $3.5 trillion tax and spending package to win over remaining lawmakers and work to quickly pass legislation to avoid a federal shutdown.

Biden’s domestic agenda is hanging in the balance, at risk of collapse and political fallout if he and Democratic leaders cannot pull their party together to deliver what could be a signature piece of legislation and the biggest overhaul of government priorities in decades.

Over the weekend, Biden personally spoke with lawmakers on possible steps, according to a White House official who requested anonymity to discuss the private conversations.

An expected Monday vote on a related $1 trillion bipartisan infrastructure package is now postponed until Thursday, amid ongoing negotiations.

More immediately, the Senate has a test vote set Monday to keep the government funded and avert a federal debt default before Thursday’s fiscal yearend deadline.

That measure stands to run into a blockade by Republican senators – ensuring lawmakers will have to try again later in the week.

The more difficult action now lies in the Senate, as Democrats are under pressure to amass the votes for Biden’s big package. It would provide an expansion of existing health, education and child care programs for Americans young and old, alongside new federal efforts to curb climate change.

Republicans are lockstep opposed to Biden’s proposal, which would be paid  for by increasing the corporate tax rate, from 21% to 26.5% on businesses earning more than $5 million a year, and raising the top rate on individuals from 37% to 39.6% for those earning more than $400,000 a year, or $450,000 for couples.

Two Democratic holdouts, Sens. Joe Manchin of West Virginia and Kyrsten Sinema of Arizona, also have said they won’t support a bill of that size. Manchin has previously proposed spending of $1 trillion to $1.5 trillion.