WASHINGTON, Jan 30 (Reuters) - Republican and Democratic members of Congress will open negotiations on Wednesday in search of a deal to fund the government and address border security, including the construction of a wall demanded by U.S. President Donald Trump.

The team of negotiators from the House of Representatives and the Senate have less than three weeks to come up with legislation to appropriate funds. The bill needs to be one that the president will accept before money runs out again on Feb. 15 or the government faces the threat of another partial shutdown.

Last week Trump agreed to temporarily re-open the federal government after a record-long 35-day shutdown even without the $5.7 billion that he had demanded from Congress to build the wall. Trump has made the long-promised border wall a key campaign promise and pledged that Mexico would pay for it.

He threatened to shut the government down again later this month if Congress cannot come up with a satisfactory deal, or said he would turn to a national emergency declaration to get the wall built -- a potential move that both Republicans and Democrats have vowed to fight.

22 PHOTOS President Trump visits border wall prototypes amid protests See Gallery President Trump visits border wall prototypes amid protests US President Donald Trump is shown border wall prototypes in San Diego, California on March 13, 2018. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) People hold signs during a protest while standing in front of the current border fence and near the prototypes of U.S. President Donald Trump's border wall, in Tijuana, Mexico March 13, 2018. The sign on the right reads "Trump, walls can be jumped over". REUTERS/Edgard Garrido US President Donald Trump inspects border wall prototypes in San Diego, California on March 13, 2018. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) People attach a sign reading "Trump, stop the mass deportations" to the current border fence and near the prototypes of U.S. President Donald Trump's border wall, during a protest in Tijuana, Mexico March 13, 2018. REUTERS/Edgard Garrido US President Donald Trump's motorcade arrives at the border fence in San Diego, California on March 13, 2018. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) People hold signs reading "No to the wall" and "Trump, put your wall, but in your territory, not in ours", during a protest near the prototypes of U.S. President Donald Trump's border wall, seen behind the current border fence, in Tijuana, Mexico March 13, 2018. REUTERS/Edgard Garrido US President Donald Trump is shown border wall prototypes with White House Chief of Staff John Kelly (L) in San Diego, California on March 13, 2018. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) A man holds a sign reading "Trump, put your wall, but in your territory, not in ours", during a protest near the prototypes of U.S. President Donald Trump's border wall, seen behind the current border fence, in Tijuana, Mexico March 13, 2018. REUTERS/Edgard Garrido US President Donald Trump arrives to inspect border wall prototypes in San Diego, California on March 13, 2018. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) People hold signs reading "No to the wall, Trump," and "Trump, we are not enemies of the USA" during a protest near the prototypes of U.S. President Donald Trump's border wall, seen behind the current border fence, in Tijuana, Mexico March 13, 2018. REUTERS/Edgard Garrido US President Donald Trump speaks during an inspection of border wall prototypes in San Diego, California on March 13, 2018. Donald Trump -- making his first trip to California as president -- warned there would be 'bedlam' without the controversial wall he wants to build on the border with Mexico, as he inspected several prototype barriers. The trip to the 'Golden State' -- the most populous in the country and a Democratic stronghold -- was largely upstaged by his own announcement that he had sacked Secretary of State Rex Tillerson. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) Mexican Federal Police officers stand guard the Mexican side of the Mexico-US border in Tijuana, Baja California state, from where prototypes of the border wall, which US President Donald Trump will inspect on the outskirts of San Diego, in the US, are visible on March 13, 2018. Fresh off a cabinet reshuffle, President Donald Trump was headed for Democratic stronghold California on Tuesday to inspect prototypes of the controversial border wall with Mexico that was the centerpiece of his White House campaign. / AFP PHOTO / GUILLERMO ARIAS (Photo credit should read GUILLERMO ARIAS/AFP/Getty Images) People hold signs reading "Trump, we will not pay for the wall" and "Trump, stop the mass deportations" near the border fence between Mexico and the U.S., in Tijuana, Mexico March 13, 2018. REUTERS/Edgard Garrido Journalists gather at a rooftop near the US -Mexico border as President Trump is expected to inspect the border wall prototypes built outskirts San Diego, in Tijuana, Baja California State, Mexico, on March 13, 2018. Fresh off a cabinet reshuffle, President Donald Trump was headed for Democratic stronghold California on Tuesday to inspect prototypes of the controversial border wall with Mexico that was the centerpiece of his White House campaign. / AFP PHOTO / GUILLERMO ARIAS (Photo credit should read GUILLERMO ARIAS/AFP/Getty Images) U.S. police officers use a ladder to climb up a truck parked in front of the prototypes of U.S. President Donald Trump's border wall, on the U.S. side of the current border fence, in Tijuana, Mexico March 13, 2018. REUTERS/Jorge Duenes An agent faces Mexico while standing by the vehicle of U.S. President Donald Trump at the border near San Diego, California, where Trump reviewed wall prototypes designed to serve as a protective barrier against illegal immigrants, drugs and smuggled weapons, March 13, 2018. REUTERS/Kevin Lamarque A U.S. Customs and Border Protection (CBP) Border Patrol Agent sits on horseback near U.S. President Donald Trump's motorcade during a tour of U.S.-Mexico border wall prototypes near the Otay Mesa Port of Entry in San Diego, California. U.S., March 13, 2018. REUTERS/Kevin Lamarque TIJUANA, MEXICO - MARCH 13:Anti-Trump protestors demonstrate on the Mexico side of the border before the arrival of the U.S. President to inspect the prototypes of the proposed border wall on March 13, 2018 in Tijuana, Mexico. (Photo by Wally Skalij/Los Angeles Times via Getty Images) The motorcade carrying US President Donald Trump drives past a US-Mexico border fence as Trump head for an inspection of border wall prototypes in San Diego, California on March 13, 2018. Donald Trump -- making his first trip to California as president -- warned there would be 'bedlam' without the controversial wall he wants to build on the border with Mexico, as he inspected several prototype barriers. The trip to the 'Golden State' -- the most populous in the country and a Democratic stronghold -- was largely upstaged by his own announcement that he had sacked Secretary of State Rex Tillerson. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) Mounted Border Patrol agents are seen as US President Donald Trump inspects border wall prototypes in San Diego, California on March 13, 2018. Donald Trump -- making his first trip to California as president -- warned there would be 'bedlam' without the controversial wall he wants to build on the border with Mexico, as he inspected several prototype barriers. The trip to the 'Golden State' -- the most populous in the country and a Democratic stronghold -- was largely upstaged by his own announcement that he had sacked Secretary of State Rex Tillerson. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) US President Donald Trump inspects border wall prototypes in San Diego, California on March 13, 2018. Donald Trump -- making his first trip to California as president -- warned there would be 'bedlam' without the controversial wall he wants to build on the border with Mexico, as he inspected several prototype barriers. The trip to the 'Golden State' -- the most populous in the country and a Democratic stronghold -- was largely upstaged by his own announcement that he had sacked Secretary of State Rex Tillerson. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) US President Donald Trump holds up a poster of before and after photos of a segment of the border wall prototypes with Chief Patrol Agent Rodney S. Scott (R) in San Diego, California on March 13, 2018. / AFP PHOTO / MANDEL NGAN (Photo credit should read MANDEL NGAN/AFP/Getty Images) Up Next See Gallery Discover More Like This HIDE CAPTION SHOW CAPTION of SEE ALL BACK TO SLIDE

Trump's fellow Republicans, who control the Senate, had stood by the president but faced increasing pressure as the impacts of the shutdown spread and public sentiment soured. Democrats, who took over the House this month after the shutdown began, remained unified in their opposition to Trump's wall.

Some top Democrats have said they are open to paying for fencing or other physical border barriers in some areas but not a wall along the entire length of the southern border.

In an early morning tweet on Wednesday, Trump warned lawmakers that they must consider his wall.

"If the committee of Republicans and Democrats now meeting on Border Security is not discussing or contemplating a Wall or Physical Barrier, they are Wasting their time!" he wrote.

Even if congressional negotiators forge a deal, it is unclear whether Trump would accept it. Negotiators, who are scheduled to meet for the first time later on Wednesday, must wrap up their work around Feb. 10 in order to pass legislation in time to meet the Feb. 15 deadline. (Writing by Susan Heavey Editing by Chizu Nomiyama)

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