A bipartisan group of lawmakers threw cold water on President Donald Trump's suggestion of a "prorated down payment" for his proposed barrier on the US-Mexico border.

"I don't know if he knows what he's talking about," House Speaker Nancy Pelosi said to reporters on Thursday. "Do you?"

Republican Sen. Lisa Murkowski of Alaska also appeared doubtful, saying "I don't know what that means."

The US government is lumbering into its sixth week in shutdown mode as President Donald Trump and congressional lawmakers look to cobble together an agreement that sends furloughed federal employees back to work and addresses Trump's desire for US taxpayer money to fund a US-Mexico border wall.

There appeared to be some movement on the issue Thursday after Trump pitched a new idea: a "prorated down payment" for the wall.

Some Republican and Democratic leaders were uninterested.

"I don't know if he knows what he's talking about, do you?," House Speaker Nancy Pelosi said to reporters on Thursday.

Republican Sen. Lisa Murkowski of Alaska was equally puzzled by Trump's down payment request: "I don't know what that means," she said.

The suggestion of a down payment comes as Senate Majority Leader Mitch McConnell and Minority Leader Chuck Schumer dug further into negotiations on Thursday. White House press secretary Sarah Huckabee Sanders indicated that in exchange for a "large down payment on the wall," Trump was willing to support a congressional plan to fund federal agencies for three weeks.

The potential down payment is supported by Republican Sen. Lindsey Graham, one of Trump's outspoken supporters, who suggested it was the only viable plan to break the stalemate.

"The way forward is clear to me: a three-week continuing resolution that includes a down payment on wall/barrier funding and priorities of Democrats for disaster relief, showing good faith from both sides," Graham said in a statement. "I strongly urge my Democratic colleagues to work with the White House on a three-week CR that includes a down payment on wall/barrier funding consistent with [Department of Homeland Security] priorities."

But Democrats balked at the suggestion, including Pelosi, who told reporters it was "not a reasonable agreement."

President Donald Trump discusses border security with Senate Minority Leader Chuck Schumer in the Oval Office. Mark Wilson/Getty Images

Democrats were also quick to point out that a Trump-supported funding bill, which included money for his barrier, received fewer votes than a separate Democrat-sponsored bill that included no funding for a wall at all.

Both bills fell short of the required 60 Senate votes to pass on Thursday. The Senate mostly voted along party lines, with the Trump-backed bill at 50-47, and the Democrats' bill at 52-44. Six Republican lawmakers broke ranks with their party, including Lamar Alexander of Tennessee, Susan Collins of Maine, Cory Gardner of Colorado, Johnny Isakson of Georgia, Lisa Murkowski of Alaska, and Mitt Romney of Utah.

"Six strong Republicans stood up for the American people and I was very proud of that," Pelosi said. "We got a bigger vote than the President's vote."

The government shutdown has affected around 800,000 federal employees and contractors, and is the longest shutdown in US history. The US Coast Guard, which operates under the purview of the Department of Homeland Security, was reportedly not able to pay around 42,000 active-duty service members last week.

As Congress searches for a path forward, the White House was reportedly preparing a draft of a national-emergency declaration that would seek to divert $7 billion from other government agencies to fund a wall. That move, if Trump follows through with it, is expected to face challenges in court.