Progressive Democrats signaled Sunday they are willing to compromise to get US President Joe Biden's sweeping domestic agenda through Congress, but a tough fight lay ahead to overcome deep party divisions.

The White House has scrambled to gain the support it needs among feuding Democrats for two massive spending packages that may well define the president's legacy.

Some Republicans support the $1.2 trillion infrastructure bill to rebuild the nation's crumbling roads, bridges and waterways, but they remain in lockstep opposition to the second package -- a $3.5 trillion spending plan that would allocate more funds for education and child care, expand health programs and promote clean energy.

Former president Donald Trump, who still wields considerable power within the Republican party, blasted the spending plan in a statement Sunday.

"The Democrat plan, if approved at any level, will push our Country towards socialism!" he said.

The dispute means Democrats, who narrowly control the Senate and House of Representatives, must unite to get Biden's giant "Build Back Better" proposal across the line -- a heavy lift on Capitol Hill where last week's game of chicken between moderates and liberals ended in stalemate.

To maintain negotiating leverage, progressives are refusing to back the popular infrastructure bill until they are assured the Senate is a "yes" on the social spending deal.

With reports emerging that moderates have proposed a $2 trillion counter-offer for that mega bill, leftist Senator Bernie Sanders said that would be insufficient for historic legislation that could reshape the American economy.

"But I accept that there's going to have to be give and take," he told ABC talk show "This Week."

Congresswoman Pramila Jayapal, leader of the House progressives, conceded heading into the weekend that her camp were going to have to lower their topline figure.

Speaking on CNN's "State of the Union" Sunday, she said there is "no number on the table yet that everyone has agreed to," but that it would realistically land "somewhere between $1.5 and $3.5" trillion.

Compromise was clearly in the air, with one proposal gaining traction, according to Jayapal and liberal congresswoman Alexandria Ocasio-Cortez, to shorten the duration of funding for the legislation's programs aimed at helping working families.

"One of the ideas that is out there is fully fund what we can fully fund, but maybe instead of doing it for 10 years, you fully fund it for five years," Ocasio-Cortez told CBS's "Face the Nation."

House Speaker Nancy Pelosi had imposed an arbitrary deadline of last week for passage of both spending bills, only to see Congress blow past it with no resolution.

In a Saturday letter she told Democrats that "more time was needed to reach our goal," and was now eyeing October 31 as a new target.

But Congress must address a high-stakes deadline before that: raising the US debt limit by October 18, when the nation will run out of money to pay its bills.

Democrats say avoiding such a catastrophic default is a top priority.

Republicans have balked at helping, however, prompting a fierce response from Biden who said it would be "unconscionable" for Republicans to refuse to raise the debt ceiling.

The White House meanwhile was holding firm to Biden's demand that the end result for his two spending packages, not the timing, was the focus.

"We're not using an artificial timeline," Biden senior advisor Cedric Richmond told Fox News Sunday. "We're concerned about delivery."

And Biden will head to Michigan Tuesday in an effort to unite public support behind the plan, the White House said, touting the goal of "investing in working families... by repealing tax giveaways to the rich."

The legislative one-two punch is under most threat in the Senate, where two moderate Democrats including Arizona's Kyrsten Sinema have stood firm against what they describe as recklessly high spending targets.

Sinema blasted House progressives Saturday for "inexcusable" brinkmanship, calling their refusal to support infrastructure until they get their way on the broader spending package "an ineffective stunt."

Still, Biden's party appeared to be slowly -- painfully -- inching towards a historic deal.

"It'll be a grind," Democratic strategist and former Barack Obama advisor David Axelrod said on Twitter, "but I bet Dems get there on both bills."