AP PHOTOS: Wall prototypes sit on the US-Mexico border AP PHOTOS: Wall prototypes sit on the US-Mexico border as Trump and congressional Democrats are in a standoff over funding for the border wall

TIJUANA, Mexico -- Border wall prototypes stand in San Diego near the Mexico-U.S. border as President Donald Trump and congressional Democrats are locked in a standoff over border wall funding that has shut down parts of the U.S. government.

The shutdown started Saturday, when funding lapsed for nine Cabinet-level departments and dozens of agencies, and threatens to carry over into January.

The impasse over government funding began last week, when the Senate approved a bipartisan deal keeping government open into February. That bill provided $1.3 billion for border security projects but not money for the wall. At Trump's urging, the House approved that package and inserted the $5.7 billion he had requested.

But Republicans in the Senate lacked the 60 votes needed to force the measure with the wall funding through their chamber. That jump-started negotiations between Congress and the White House, but the deadline came and went without a deal.

Trump, who was elected in 2016, campaigned on a promise to build a "big, beautiful wall" made of concrete, rebar and steel across the length of the southern border. He said he would make Mexico pay for it, but Mexico has refused.

Lawmakers have limited the administration to replacing or strengthening existing barrier designs, rather than building Trump's new wall prototypes.

In budget year 2017, Congress provided $292 million to the Department of Homeland Security to build a steel-bollard wall to replace "ineffective" barriers along the border with Mexico. More than 31 of 40 miles have been constructed, and nine more are scheduled to be completed by 2019.

In March, Congress also approved funding for 84 miles (135 kilometers) of construction along the southern border.