Meanwhile, America's government shutdown - now in Day 7 - will likely carry into next week and the new year as Congress refuses to budge in the standoff. Time to get tough on Border Security.
Mulvaney said Trump is willing to shut down the border, despite the economic hit as $558 billion worth of goods flowed across the border past year, because "all options are on the table" and "it's the only way we can get the Democrats' attention".
"I'm not going to negotiate in the press, but the president has been willing to negotiate on this point and the Democrats have not been willing to do anything", Sanders said. The closures began last Saturday after Republicans and Democrats were unable to agree on a funding package that would keep the government open and fund Trump's promised border wall.
The White House is accusing Democrats of walking away from the negotiating table.
Disputes with Congress over funding for the border wall have already led to a partial US government shutdown.
The shutdown is idling hundreds of thousands of federal workers and beginning to pinch citizens who count on some public services.
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Almost a week into a U.S. Democrats said the White House offered $2.5 billion for border security, but that Senate Democratic leader Chuck Schumer told Vice President Mike Pence it wasn't acceptable.
Trump canceled his Christmas trip to Florida and remained in the White House, saying on Christmas Eve that he was "waiting for the Democrats to come back and make a deal".
At that point, he could face a politically hard choice - back down on his full wall-funding demand or veto the bill and single-handedly extend the partial shutdown.
Mulvaney added of the shutdown: "We do expect this to go on for a while". "We're going to behave like adults and do our job".
If he chose the latter, putting his personal stamp on the shutdown, Congress might then move to override his veto, but that would take a two-thirds vote in both the Senate and the House, a challenging hurdle for lawmakers.
He has also repeatedly threatened to cut off USA aid to countries he deems insufficient partners in combating illegal immigration, but has thus far failed to follow through with those threats.