Washington (CNN) Pressure has been intensifying for days on the Senate to pass a massive stimulus package to respond to the economic fallout of the coronavirus , but Monday came and went without much action.

After four straight days of marathon negotiations, the Trump administration and senators again failed to secure an agreement on a roughly $2 trillion plan to provide a jolt to the economy and give aid to hard-hit workers and industries.

But leaders emerged from late-night meetings in the Capitol optimistic that a deal could be struck Tuesday despite tweets from President Donald Trump trashing the deal and baselessly accusing Democrats of siding with "the virus."

Treasury Secretary Steven Mnuchin, who has been negotiating the deal, remained optimistic and said late Monday, "We are hopeful that this could be closed out tomorrow."

Earlier in the evening, Senate Majority Leader Mitch McConnell had said there would be no further votes in the Senate Monday as negotiations continued into the night to reach a bipartisan deal on what is likely to be the most significant legislative response to fallout from the pandemic so far.

Lawmakers have already passed two other major legislative packages in response to the outbreak, and the current legislation is being referred to as "phase three" in the legislative response.

But coming to a deal on such a massive package has been trickier, and the inability to reach and vote on a deal by Monday evening -- let alone by the Senate's self-imposed weekend deadline -- has underscored a tense divide between Republicans and Democrats.

Democrats have repeatedly blocked efforts to advance the stimulus because of concerns that it prioritizes corporate industry over American workers. Republicans have argued that Democrats are stalling critical economic relief amid the devastating spread of coronavirus.

The differences are narrow, according to Senate Minority Leader Chuck Schumer, Mnuchin and White House legislative director Eric Ueland, who departed the Capitol shortly before midnight after spending 15 hours in the building on Monday. The three engaged in intense negotiations, meeting six times in Schumer's office, with Mnuchin and Ueland also meeting separately several times with McConnell to see what he would be willing to support.

Mnuchin said that he spoke 10 times with Trump through the course of the day to carry out his request for a deal to be reached. He said he planned to be back in the Capitol at 9:30 a.m. ET Tuesday.

"I think we've made a lot of progress. Both sides have been working around the clock," Mnuchin said. "Still documents that are going to be reviewed tonight and turned around and there are still a couple of open issues but I think we're very hopeful this can be closed out tomorrow."

Asked about a tweet from Trump earlier in the evening criticizing Democrats on their handling of the stimulus talks, Mnuchin said, "I think the President was commenting on a lot of the issues that the House added in that they'd like to have."

Schumer said that Trump seemed "very happy" that they were getting close to a deal.

"It's a huge bill of $2 trillion, with many different moving parts," Schumer said, when asked why they are having difficulty closing out a deal. He said he was pleased the deal seemed to preserve the money for hospitals he was seeking. "That's the expectation, that we will finish it tomorrow and hopefully vote on it tomorrow evening."

Asked if he would support a bill that House Speaker Nancy Pelosi doesn't also back, Schumer said: "I'm telling you what I said and that's it."

After announcing there wouldn't be any more votes Monday evening, McConnell signaled this could drag on until at least the middle of the week. He took the procedural steps to set up another vote as late as Wednesday to consider the stimulus plan. In reality, however, if there's a deal between Schumer and the White House, a vote could happen as soon as Tuesday.

Some GOP senators said earlier Monday that the list of differences had narrowed.

"The list is getting shorter, but we aren't going to have a deal today... Even if they got a deal late tonight, there wouldn't be time to line it up and vote on it, so we will be here tomorrow," Sen. John Cornyn of Texas said.

But tensions came to a head earlier in the day when Senate Democrats blocked a procedural vote to move forward with a stimulus plan for the second day in a row. Democrats have argued that McConnell should not be holding what they have called "arbitrary" votes while negotiators are still attempting to reach a bipartisan deal.

The vote on Monday, like the vote on Sunday, was a procedural attempt to limit debate on a shell bill that McConnell is using as a placeholder until negotiators reach a consensus deal. If it had succeeded, it would have cleared the way for the Senate to set up a final vote on a stimulus deal.

Republicans have been urging swift passage, especially after coronavirus struck one of their own and led two others to go into self-quarantine over the weekend.

Senate Majority Whip John Thune criticized Democrats for holding things up by trying to add more to the bill.

"If they could get the list narrowed down to the handful of items that really need to be negotiated, that would be great. But I think the Dems consistently are bringing new things, you know, new asks and demands in, and so much of their agenda, like I said, has nothing to do with coronavirus. They want to achieve a lot of their wish list through this crisis, which is really unfortunate," the South Dakota Republican said.

That frustration is now coming from both sides of the aisle.

Sen. Doug Jones, a moderate Alabama Democrat up for reelection this year, voted with Republicans to advance the stimulus bill on Monday after voting "no" in the first procedural vote that took place Sunday. He told CNN that he was "embarrassed" by the political games he said both sides are playing. The Democratic senator said that negotiators had made "a lot of progress," but that McConnell shouldn't have forced the vote while negotiations are ongoing.

One key holdup appears to still be roughly $500 billion in funds for loans and loan guarantees for distressed companies, states and localities without enough guidelines or oversight to satisfy Democrats. They want to ensure that any bailout for large companies will primarily benefit workers. But pushback from Democrats has centered on not only the substance of the legislation, but on the process that Republicans used to come up with it as well, arguing that they were locked out of negotiations at the start.

McConnell has defended his approach, telling CNN's Dana Bash Thursday, "Republicans are in the majority in the Senate. We wanted to put forward our proposal. We feel like we have an obligation to do that as a majority and the Democrats, of course, need to be given an opportunity to react to it."

Senators have been working day and night to negotiate a deal, but despite marathon negotiations, lawmakers missed their own deadline of wrapping up legislation before the end of the weekend. The scale of the package -- which has grown by over a trillion dollars over the course of several days -- underscores the recognition of the urgency brought on by the accelerating spread of the coronavirus pandemic that has all but shuttered the American economy over the last week.

Schumer struck an optimistic tone ahead of Monday afternoon's procedural vote that a bipartisan deal could be reached shortly.

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

Schumer also signaled that once a deal is reached, the Senate could move quickly to hold a final vote.

"Once we have an agreement that everyone can get behind we're prepared to speed up the consideration of that agreement on the floor," he said.

McConnell harshly criticized Democrats in his own remarks ahead of the vote, arguing that they are trying to push through unrelated priorities and are holding up a deal as a result.

"The markets are tanking once again because this body can't get its act together," he said. "This has to stop," McConnell said, adding, "The country is out of time."

In another sign of tension between Democrats and Republicans, House Democrats are also pressing forward with plans for their own third coronavirus response legislation, an effort that only adds to the pressure on the Senate to reach a consensus deal sooner rather than later.

Sunday's failed vote came on the same day that the first US senator -- Sen. Rand Paul of Kentucky -- tested positive for coronavirus, which raised questions about how long lawmakers will continue to be able to proceed with business as usual in the Capitol building and prompted two other Republican senators -- Mike Lee and Mitt Romney of Utah -- to self-quarantine

This story has been updated with additional developments Monday.