The president is “willing to do whatever it takes” to push through the contentious $5.7bn (£4.3bn) project, Mick Mulvaney warned as hundreds of thousands of federal staff prepared to return to work.
Mr Trump signed off a spending bill on Friday to reopen shuttered government departments until 15 February.
While the deal ended the longest government shutdown in history and meant workers could be paid for the first time this year, the prolonged stand-off between the president and Democrats shows no sign of drawing to a close.
Mr Trump has continued to insist on building a wall along the US-Mexico border, a project congressional Democrats consider an ineffective and unethical waste of money.
A group of 17 Republican and Democrat politicians has been set up to thrash out a compromise, but on Sunday the president told the The Wall Street Journal the odds of them agreeing a deal he would sign off were “less than 50-50”.
Another shutdown was “certainly an option,” he added, vowing to declare a national emergency to secure funding for the wall if necessary.
The first shutdown cost the US economy at least $6bn (£4.6bn) in just over a month, according to the S&P Global Ratings.
Asked if the president would be prepared to partially close down the government again if no agreement has been reached by 15 February, Mr Mulvaney told CBS News: “Yeah I think he actually is. Keep in mind he’s willing to do whatever it takes to secure the border. He does take this very seriously.”
The White House chief of staff added: “He doesn’t want to shut the government down, let’s make that very clear. He doesn’t want to declare a national emergency. At the end of the day, the president’s commitment is to defend the nation and he will do it with or without Congress.”
Mr Trump has indicated he would be unlikely to accept less than $5.7bn funding for the border wall, one of his key campaign promises ahead in the 2016 election. He said would also be wary of any proposed deal that exchanged wall funding for broad immigration reform.
Kevin McCarthy, the leading Republican in the House of Representatives, said Democrats had funded border barriers in the past and claimed they were refusing this time simply because the demand was coming from Mr Trump.
But Hakeem Jeffries, a member of the Democratic leadership in the House, said his colleagues were looking for “evidence-based” legislation.
“Shutdowns are not legitimate negotiating tactics when there’s a public policy disagreement between two branches of government,” he added.