Trump's Twitter threat introduced a fresh wild card for congressional negotiators to deal with as the remaining legislative days tick down before government funding runs out -- an explosive prospect for both parties with just 100 days until

Trump has previously floated the possibility of a government shutdown over border security and immigration, and on Sunday he made his threat explicit, saying he would do so unless Congress funds his proposed wall, which he promised Mexico would pay for, and puts in place his preferred immigration policies.

In May, Trump suggested "closing up the country for a while" if he did not get his wall.

"They don't want the wall," Trump said. "But we're going to get the wall, even if we have to think about closing up the country for a while."

Sunday's shutdown threat from Trump also echoed a remark he made in February when he said "I'd love to see a shutdown" if the government did not agree to address immigration.

"I said to Congress, I will never sign another bill like this again," Trump said in March.