By CATHERINE LUCEY and LISA MASCARO
Associated Press

WASHINGTON (AP) - With no breakthrough in sight to end the partial government shutdown, President Donald Trump plans a Tuesday night address to the nation and a Thursday visit the U.S.-Mexico border to highlight his demands for a border wall. Newly empowered House Democrats - and at least a few Republican senators - are stepping up pressure on Trump and GOP lawmakers to reopen the government.

Trump said he would discuss the "Humanitarian and National Security crisis on our Southern Border" at 9 p.m. EST. He maintains that more than $5 billion for a wall is necessary to secure the border. White House press secretary Sarah Huckabee Sanders tweeted Monday that Trump will use the visit to "meet with those on the front lines of the national security and humanitarian crisis."

As the shutdown lurched into a third week, many Republicans watched nervously from the sidelines as hundreds of thousands of federal workers went without pay and government disruptions hit the lives of ordinary Americans.

Trump has offered to build the barrier with steel rather than concrete, billing that as a concession to Democrats' objections to a solid wall. They "don't like concrete, so we'll give them steel," he has said.

But the Democrats have made clear they see a wall as immoral and ineffective and prefer other types of border security funded at already agreed-upon levels.

White House officials affirmed Trump's funding request in a letter to Capitol Hill after a meeting Sunday with senior congressional aides led by Vice President Mike Pence at the White House complex yielded little progress. The letter from Office of Management and Budget Acting Director Russell Vought sought funding for a "steel barrier on the Southwest border."

The White House said the letter, as well as details provided during the meeting, sought to answer Democrats' questions about the funding request. Democrats, though, said the administration still failed to provide a full budget of how it would spend the billions requested for the wall from Congress. Trump campaigned on a promise that Mexico would pay for the wall, but Mexico has refused.

The administration letter includes a request for $800 million for "urgent humanitarian needs," a reflection of the growing anxiety over migrants traveling to the border - which the White House said Democrats raised in the meetings. And it repeats some existing funding requests for detention beds and security officers, which have already been panned by Congress and would likely find resistance among House Democrats.

House Speaker Nancy Pelosi intends to begin passing individual bills to reopen agencies in the coming days, starting with the Treasury Department to ensure Americans receive their tax refunds. That effort is designed to squeeze Senate Republicans, some of whom are growing increasingly anxious about the extended shutdown.

Among the Republicans expressing concern was Sen. Susan Collins, R-Maine, who said Senate Majority Leader Mitch McConnell should take up bills from the Democratic-led House.

"Let's get those reopened while the negotiations continue," Collins said on NBC's "Meet the Press."

Adding to concerns, federal workers might miss this week's paychecks. Acting chief of staff Mick Mulvaney said on NBC's "Meet the Press" that if the shutdown continues into Tuesday, "then payroll will not go out as originally planned on Friday night."

Over the weekend, the federal agency tasked with guaranteeing U.S. airport security acknowledged an increase in the number of its employees calling off work. But Trump and the Department of Homeland Security pushed back on any suggestion that the call-outs represented a "sickout" that was having a significant effect on U.S. air travel.

At the White House, on Monday, spokeswoman Mercedes Schlapp complained that Democratic leaders have yet to define what they mean when they say they are for enhancing border security.

"Democrats want to secure the border? Great. Come to the table," she said. "We are willing to come to a deal to reopen the government."

Trump reaffirmed that he would consider declaring a national emergency to circumvent Congress and spend money as he saw fit. Such a move would seem certain to draw legal challenges.

Incoming House Armed Services Committee Chairman Adam Smith, D-Wash., said on ABC's "This Week" that the executive power has been used to build military facilities in Iraq and Afghanistan but would likely be "wide open" to a court challenge for a border wall. Speaking on CNN's "State of the Union," Intelligence Committee Chairman Adam Schiff called the idea a "nonstarter."

Trump asserted that he could relate to the plight of the hundreds of thousands of federal workers who aren't getting paid, though he acknowledged they will have to "make adjustments" to deal with the shutdown shortfall.

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