Democrats and Republicans continue to negotiate terms on a massive stimulus package, two Senate aides told CNBC. The measure again failed a key procedural vote in the Senate on Monday afternoon, as there were major differences between the two parties over what to include in the final legislation.

The delay could make it difficult for Trump to sign a bill this week. Senate rules mandate that a cloture vote has to "ripen" for one full day before it the Senate can vote, unless the currently quarreling Senate unanimously decides to hold a vote sooner. Three-fifths of the Senate must vote for cloture in order to end debate and move the bill along.

The measure has a price tag of well over $1 trillion and is intended to limit the economic pain from the coronavirus outbreak. The effort has taken on urgency as hospitals, workers, people, and companies have all pleaded they need cash quickly to cope with the crushing economic impact of the coronavirus.

Treasury Secretary Steven Mnuchin told CNBC that Monday "we need to get this deal done today." But the talks have been marred by partisan disagreement. The bill previously failed to clear a procedural hurdle in the Senate on Sunday and again Monday afternoon.

Senate Democrats have criticized the $500 billion fund that the Republican proposal sets aside for distressed businesses, calling it a bailout fund "with no strings attached." Democrats are also seeking enhanced unemployment measures and protections for workers. GOP lawmakers slammed Democrats for seeking climate provisions within the measure, as well. House Speaker Nancy Pelosi floated her own proposal for a stimulus bill Monday.

Senate Minority Leader Chuck Schumer nonetheless was optimistic earlier Monday, seeing he believed the two parties could come to an agreement by the end of the day.

"We're very close to reaching a deal. Very close. And our goal is to reach a deal today," he said. "And we're hopeful, even confident that we will meet that goal."

He said two parties had come to certain agreements about revisions to the Republicans' bill, including adding more unemployment protections and adding more money to hospitals. He said the Democrats are "fighting hard and making progress" on more funding for state and local governments.

Stocks cut their losses on Schumer's optimistic words. But the Dow Jones industrial average ultimately closed 3% lower, at one point giving away all of its gains since President Donald Trump's election.

After the second procedural vote failed, McConnell threw aside his usually placid appearance as he tore into Senate Democrats for the second straight day on Monday, accusing them of filibustering a deal the country needs immediately. He accused Democrats of adding to their wish list, rather than focusing on getting out a deal quickly.