As President Donald Trump takes his call for funding for a border wall to the border city of El Paso, Texas on Monday evening, House-Senate negotiators are struggling to finalize a 2019 funding deal on border security and the operations of the Department of Homeland Security, raising the possibility of another partial government shutdown at the end of this week if no agreement can be reached.

"The Border Committee Democrats are behaving, all of a sudden, irrationally," the President said in one of a flurry of tweets aimed at Democrats on the border security talks and funding for the wall on Sunday.

"They are offering very little money for the desperately needed Border Wall & now, out of the blue, want a cap on convicted violent felons to be held in detention," Mr. Trump tweeted.

The latest stumbling block in negotiations was not over money for a border wall - which the President seemed unlikely to get - but rather an insistence by Democrats to limit the number of people who could be held by federal immigration authorities.

"A cap on ICE detention beds will force the Trump administration to prioritize deportation for criminals and people who pose real security threats, not law-abiding immigrants who are contributing to our country," said Rep. Lucille Roybal-Allard (D-CA), a top Democratic negotiator.

In a statement issued Sunday evening, Roybal-Allard characterized the dispute as one which does not center on new illegal immigrant arrivals, but rather on expanded efforts by immigration authorities under the Trump Administration to find people who are living illegally in the U.S., and deport them.

"A cap on detention beds associated with interior enforcement will rein in the Trump administration’s deportation agenda," the California Democrat added.

Republicans were quick to reject that idea.

"Reducing detention bed space for violent offenders for more wall funding is a bad, dangerous deal," said Sen. Lindsey Graham (R-SC).

Congressional leaders had originally hoped a deal could be finalized on Friday; then the goal was sometime this weekend, or maybe by Monday.

But as the President was tweeting from the White House on Sunday night, the outlook seemed to be turning against an agreement, again opening the possibility of a second partial shutdown, which could impact some 800,000 federal workers.

"For thirty-five days, President Trump shut down the government to bully Congress into giving him a border wall that Democrats and Republicans alike oppose," said House Majority Leader Steny Hoyer (D-MD).