WASHINGTON – The partial government shutdown stretched into its third week on Saturday as President Donald Trump seemed to dig in on demands for added border security – signaling again that the standoff could go on for a long time.

A meeting between top White House officials, including Vice President Mike Pence, and senior congressional aides ended after hours of discussions without any agreement that could end the 15-day shutdown. Another meeting is scheduled for Sunday, but to many on Capitol Hill, there doesn't appear to be an end in sight.

Throughout the day, the president persisted in his efforts to blame Democrats for the shutdown in a barrage of tweets, making the case for a U.S.-Mexico border wall by saying everyone besides "drug dealers, human traffickers and criminals" wants one.

"The Democrats could solve the Shutdown problem in a very short period of time," Trump wrote on Twitter early Saturday. "All they have to do is approve REAL Border Security (including a Wall), something which everyone, other than drug dealers, human traffickers and criminals, want very badly! This would be so easy to do!"

Trump also claimed that most of the thousands of federal employees who are working without pay during the shutdown are liberals, writing on Twitter: "I don’t care that most of the workers not getting paid are Democrats, I want to stop the Shutdown as soon as we are in agreement on Strong Border Security!"

Pence, Homeland Security Secretary Kirstjen Nielsen and senior adviser Jared Kushner, the president's son-in-law, met with top congressional aides at the Eisenhower Executive Office Building to negotiate an end to the shutdown.

After talking for several hours, the meeting concluded without any agreement, thus allowing the shutdown to slide into Sunday for a 16th day – tying it for the third-longest shutdown in U.S. history.

After being briefed on the meeting, the president wrote on Twitter that "not much headway" was made and again stuck by his border security demands. The vice president's office, meanwhile, called the talks on Saturday "productive" adding that another meeting was scheduled for Sunday.

Pence's office said that there was not an in-depth conversation about a dollar figure for a border wall but rather a conversation about making border security a priority. Pence's office said the vice president also reiterated Trump's position and said Democrats requested more details in writing on the needs of Homeland Security.

Democrats, on the other hand, signaled the more than $5 billion Trump wants to construct a wall was a big focus of the discussions.

"Democrats in the room asked for a formal budget justification for the administration’s position in order to finally determine what the administration’s request is," a Democratic source familiar with the meeting told USA TODAY. "Today was an opportunity for the administration to come down from an untenable position that cannot pass the Congress. That did not happen."

Instead, another source said, the administration "doubled down on their partisan proposal that led to the Trump shutdown in the first place," according to a Democratic aide familiar with the meeting.

"Democratic staff repeatedly urged the Trump administration and Republicans to reopen the government but were rejected," the aide told USA TODAY. "Democratic staff indicated it will be difficult to make real progress as long as the president keeps the government closed."

Despite the disagreements, the meeting did not appear as contentious as the one held Friday with the president and top Democrats at the White House where Trump said he was prepared to allow parts of the government to remain shuttered for months or even years if that’s what it takes to get the funding he wants for a border wall along.

After the Friday meeting, Trump stressed during a Rose Garden news conference that he doesn’t believe a shutdown would drag on that long. “But I am prepared,” he said. "I will do whatever I have to do," he said.

Trump also floated the possibility of declaring a national emergency to secure the border wall funding “for the security of our country.”

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The House and the Senate both adjourned Friday and aren’t scheduled to return to Washington until Tuesday afternoon, meaning that the earliest shuttered departments and agencies could reopen would be Wednesday.

If the shutdown is still in effect on Wednesday, that will mark its 19th day, making it the second-longest on record.

House Speaker Nancy Pelosi, R-Calif., said Saturday that House Democrats would introduce bills next week to fund parts of the government that are currently part of the shutdown, including the Treasury Department and IRS.

"This action is necessary so that the American people can receive their tax refunds on schedule," Pelosi said. "The certainty of the tax returns of hard-working families should no longer be held hostage to the president’s reckless demands."

In its policies, the IRS has categorized issuing tax refunds as a "non-excepted" activity – meaning those tasked with processing refunds would be furloughed during a shutdown and millions of Americans wouldn't get their checks on time.

The shutdown began on Dec. 22, when nine federal departments and several smaller agencies – representing a quarter of the federal government – ran out of money and had to close their doors because of a budget dispute between the White House and Congress. Some 800,000 federal employees have been forced to go on unpaid leave or work without pay.

The sticking point has been Trump’s insistence on more than $5 billion in funding for a border wall. Democrats refuse to give him the money, arguing that a wall would be expensive, wasteful and ineffective.

Late Thursday, on their first day back in the majority, Pelosi and House Democrats pushed through a package of spending bills to reopen the government. But in the GOP-led Senate, Majority Leader Mitch McConnell, R-Ky., dismissed the legislation as “political theater, not productive lawmaking” and said he would not put the package to a vote because Trump would not sign it.

The longest government shutdown on record lasted 21 days and lasted from Dec. 5, 1995, to Jan. 6, 1996. The battle involved a dispute between President Bill Clinton and Republican House Speaker Newt Gingrich over spending cuts. That shutdown ended when the two sides agreed to a seven-year budget plan with some spending cuts and tax increases.