By MATTHEW DALY and CATHERINE LUCEY, Associated Press

WASHINGTON (AP) — Arguing heatedly in public with Democratic leaders, President Donald Trump threatened repeatedly on Tuesday to shut down the government if Congress doesn't provide the money he says is needed to build a wall at the Mexican border. He insisted the military can build it if Democrats won't vote for the funding.

Trump's comments came as he opened a contentious meeting with Democratic Senate and House leaders Chuck Schumer and Nancy Pelosi, with the government looking at a possible partial shutdown on Dec. 21 when funding for some agencies will expire.

Schumer and Pelosi both said legislation to keep the government open and provide additional border security could pass both houses of Congress, but Trump said major wall funding was necessary.

Schumer said, "You say 'my way or we'll shut down the government.'" Trump responded that border security was necessary and a wall was necessary for border security.

"Yes, if we don't get what we want ... I will shut down the government," he declared.

Constantly interrupting, Trump squabbled with the Democrats over whether wall funding could be approved in the House or Senate without Democratic votes.

"This has spiraled downwards," Pelosi said.

The president asked whether Republicans had won the Senate in the November election.

"When the president brags he has won North Dakota and Indiana, he's in real trouble," retorted Schumer with a smile.

In a series of tweets earlier Tuesday, Trump said immigration and border patrol agents and thousands of active-duty service members he sent to the border have done a "FANTASTIC" job. But he said "A Great Wall would be, however, a far easier & less expensive solution."

Trump said he looked forward to meeting with Schumer and Pelosi, but claimed they don't want border security for "strictly political reasons."

"If the Democrats do not give us the votes to secure our Country, the Military will build the remaining sections of the Wall. They know how important it is!" Trump said.

Schumer and Pelosi said Monday that Republicans have the power to keep the government open since they control Congress and the White House.

"Our country cannot afford a Trump Shutdown," they said in a statement, adding that Trump "knows full well that his wall proposal does not have the votes to pass the House and Senate and should not be an obstacle to a bipartisan agreement."

Republican congressional leaders have repeatedly said it's up to Trump to cut a deal with Democrats, an acknowledgment of their inability to produce spending bills with Republican votes alone.

That gave Democrats some momentum heading into the closed-door talks, which also could veer into bipartisan bills on criminal justice reform and reauthorizing farm programs.

By far, the biggest unresolved issue is the border wall. Trump wants the next funding package to include at least $5 billion for it, an idea Democrats have flatly rejected.

Pelosi and Schumer have urged Trump to support a bill that includes a half-dozen government funding bills largely agreed upon by lawmakers, along with a separate measure that funds the Department of Homeland Security at current levels through Sept. 30. The homeland bill includes about $1.3 billion for fencing and other security measures at the border.

If Trump rejects that, Democrats will likely urge a continuing resolution that funds all the remaining appropriations bills at current levels through Sept. 30, an aide said. The aide was not authorized to discuss strategy by name and requested anonymity.

Trump said Friday that Congress should provide all the money he wants for the wall and called illegal immigration a "threat to the well-being of every American community." At an appearance in Kansas City, Missouri, Trump accused Democrats of playing a political game and said he ultimately would win.

Pelosi, who is seeking to become House speaker when the new Congress convenes in January, said she and many other Democrats consider the wall "immoral, ineffective and expensive" and noted that Trump promised during the 2016 campaign that Mexico would pay for the wall, an idea Mexico has repeatedly rejected.

Schumer said Democrats want to work with Trump to avert a shutdown, but said money for border security should not include the concrete wall Trump has envisioned. Instead, the money should be used for fencing and technology that experts say is appropriate, he said.

"We do not want to let a Trump temper tantrum govern our policies or cause the shutdown of a government, which everyone on both sides of the aisle knows is the wrong idea," Schumer said. If Trump "wants to shut down the government over Christmas over the wall, that's his decision," he said.

Rep. Bennie Thompson, D-Miss., the incoming House Homeland Security chairman, said using the military to build the wall "just doesn't make any sense. I can think of a lot more important things we can do with the military then build a fence," he said Tuesday.

Vermont Sen. Patrick Leahy, the top Democrat on the Senate Appropriations Committee, said Trump is the only obstacle between fully funding the government and a shutdown.

"Time and again, President Trump has used the government of the American people as a bargaining chip for his fabricated solution to his manufactured crisis," Leahy said Monday in a Senate speech.

Trump "wants to score a made-for-reality-TV moment and he doesn't care how many hardworking Americans will suffer for it," Leahy said. "This is not about border security. This is about politics, pure and simple."

House Majority Whip Steve Scalise, R-La., said Democrats were the ones playing politics.

If Democrats have a better way to secure the border than Trump's $5 billion plan, "they need to come with an alternative," Scalise said Monday on Fox News Channel. "They can't come and say they want to shut the government down for no reason because they don't want border security. They'll lose that argument with the American people."

Associated Press writers Lisa Mascaro and Alan Fram contributed to this report.