Donald Trump has threatened to shut down the government in order to secure funding to build his controversial wall along the border with Mexico.
The president's efforts to build a barrier along America's southern border have stalled in Congress, where many lawmakers question whether his main campaign promise is really necessary.
The House has passed a spending bill with funding for the costly project, but it faces an uncertain future in the Senate.
But with a budget battle looming, Mr Trump said he would be willing to do what it takes to secure the necessary funding.
Addressing a rally crowd in Phoenix in the border state of Arizona, the US president said he had a message for "obstructionist" Democrats.
Republicans control Congress, but here is Trump pledging to shut down the government in order to build the wall. pic.twitter.com/fk0o6geJfC— CAP Action (@CAPAction) August 23, 2017
"If we have to close down our government, we're building that wall," Mr Trump said. "We're going to have our wall. The American people voted for immigration control. We're going to get that wall."
He also accused Democrats of putting American security at risk for not supporting the proposal.
The wall was one of Mr Trump's most popular campaign vows, prompting frequent rally chants of "Build that wall!"
The president had promised Mexico would pay for the barrier, but Mexico has so far refused.
Mr Trump has asked for $1.6 billion to begin construction of the wall, with Congress under pressure to pass some kind of spending bill to keep the government open after September 30.
Republicans in Congress haven’t shown much appetite for fighting to spend potentially billions more on a border barrier either. The funding would add to the deficit at the same time Republicans are trying to figure out how to pay for tax cuts.
The issue could get wrapped up with legislation to raise the federal government’s debt limit, which needs to be raised between late September and mid-October to avoid a default.
One option being considered by GOP leaders is attaching a debt limit measure to the stopgap spending bill that will likely be considered next month. Under that scenario, Mr Trump’s threat to shut down the government over the border wall could entangle the debt ceiling debate.
Earlier in the day, Mr Trump visited the border region in Yuma, where he toured a US Border Patrol operations base.
It was part of an effort to make the case that a barrier along the 2,000 mile desert-scarred frontier would stem the flow of migrants from the south.
Yuma "was once one of the least secure border areas in America (and) is now one of the most secure areas because of these investments in border security," a senior administration official said ahead of Mr Trump's trip.
A failure to secure funding for the scheme would be another setback for a president who has seen his message overshadowed by controversy and his agenda thwarted by legislative missteps.