WASHINGTON, April 24 (Reuters) - U.S. President Donald Trump tried to press Democrats on Monday to include funds for his controversial border wall with Mexico in spending legislation as lawmakers worked to avoid a looming shutdown of the federal government.
The battle offers the Republican president, whose approval ratings have slid since he took office, a chance to score his first big legislative win or to be mired in a Washington stalemate as he marks 100 days in the job on Saturday.
Republicans control both chambers of Congress, but a White House-backed bill to gut former President Barack Obama's Affordable Care Act, popularly known as Obamacare, failed to gather full party support and imploded last month.
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If no deal is agreed on spending, parts of the federal government will shut down at 12:01 a.m. (0401 GMT) on Saturday. Trump is demanding that Congress include funds for the construction of the wall, which he made a key theme of his 2016 presidential campaign and which he says will stem the flow of illegal immigrants and drugs into the United States.
The funding bill will need 60 votes to clear the 100-member Senate, where Republicans hold 52 seats, meaning at least some Democrats will have to get behind the bill.
"The Wall is a very important tool in stopping drugs from pouring into our country and poisoning our youth (and many others)! If ... the wall is not built, which it will be, the drug situation will NEVER be fixed the way it should be!" Trump tweeted on Monday.
Trump has said Mexico will repay the United States for the wall if Congress funds it first. But the Mexican government is adamant it will not finance a wall and Trump has not laid out a plan to compel Mexico to pay. Department of Homeland Security internal estimates have placed the total cost of a border barrier at about $21.6 billion.
Aside from inflaming relations with a major trading partner, the planned wall has angered Democrats. They showed no sign of softening their opposition on Monday and sought to place responsibility for any shutdown squarely on Trump and congressional Republicans.
"We were right on the path to getting something done, a good thing that both parties could support, and he throws a monkey wrench in," Senate Minority Leader Chuck Schumer told MSNBC in an interview. "That's not the way to govern."
Republican aides in Congress said negotiations on a bill to fund the government from April 28 to Sept. 30 were continuing, but they provided no timetable for unveiling legislation, or guarantees that such a bill could be passed.
A Democratic congressional aide close to the negotiations said there were no breakthroughs over the weekend toward a deal. A shutdown would have far-reaching consequences, ranging from the furlough of many federal workers to the closing of national parks.
One senior Republican congressional aide said that if not enough progress is made by Thursday, Congress would likely have to try to push forward a stop-gap spending bill to keep the government operating while negotiations continue. Leading Democrats have said they would support such a measure only if there was progress in the private talks.
Analysts said other key parts of Trump's agenda, including a proposal to cut corporate and individual income taxes, could be endangered if Republicans and Democrats fail to agree on a measure to fund the government, known as a continuing resolution.
"If Republicans struggle to pass a CR, we think it signals that the party will struggle to pass a budget resolution later in the year and the budget resolution is a prerequisite to passing tax reform via reconciliation rules," Brian Gardner, a policy analyst at financial firm Keefe Bruyette & Woods, said in a research note. He was referring to using a procedure that would allow Republicans to win legislation without Democratic support that normally would be needed in the Senate.
Trump said last week he plans a big announcement on Wednesday on tax reform. An administration official said it would consist of "broad principles and priorities."
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A Republican congressional aide said over the weekend that Democrats may agree to some aspects of the border wall, including new surveillance equipment and access roads, estimated to cost around $380 million.
"But Democrats want the narrative that they dealt him a loss on the wall," the aide said, adding it would be difficult to bring any of the minority party on board with new construction on the southwest border.
It is unclear whether Trump would sign a deal that did not include money for the wall.
On Sunday, he appeared to dangle the prospect of funding some elements of Obamacare in exchange for Democrats' support in the spending talks. He tweeted that the 2010 healthcare restructuring, which was Obama's signature domestic achievement and which enabled millions more Americans to secure healthcare coverage, could fail sooner than thought without an infusion.
The White House says it has offered to include $7 billion in Obamacare subsidies that allow low-income people to pay for health insurance in exchange for Democratic backing for $1.5 billion in funding to start construction of the barrier.
Last month's failure to repeal and replace Obamacare, a goal of most Republicans since the law was passed seven years ago, dealt a major blow to Trump. His national approval rating hovered around 43 percent in the latest Reuters/Ipsos polling. (Reporting by Julia Edwards Ainsley; Additional reporting by Susan Heavey, Doina Chiacu and Richard Cowan; Writing by Paul Simao; Editing by Frances Kerry)