Back at the White House after his historic walk across the border into North Korea, President Donald Trump on Monday quickly settled down to domestic business, signing into law a $4.6 billion bipartisan funding plan to deal with humanitarian needs for the detention of illegal immigrants, while also calling on Democrats in Congress to cut a deal on changes to underlying U.S. immigration laws.

"We're the only ones in the world who have a system like this," the President told reporters in the Oval Office. "It's absolutely insane."

Mr. Trump again said asylum reforms must be included in any legislative package approved by Congress to tighten laws dealing with illegal immigration, as he denounced what he said were 'frivolous' asylum applications by those apprehended along the southern border.

"They're totally bogus claims," the President said, as he made clear that he was ready to start delayed immigration raids after the July Fourth weekend.

"After July 4th, a lot of people are going to be brought back out," the President said.

Taking questions from reporters as he signed the border supplemental funding into law, Mr. Trump went out of his way to praise the Mexican government for doing more to stop Central Americans from making their way to the southern border of the United States.

"They're doing a very good job," the President said to reporters of Mexico. "I'm very pleased with the job they're doing," as Mr. Trump said there was no need for him to threaten additional tariffs on Mexico at this point, because the government was helping him on immigration issues.

The President's comments came as a group of House Democrats toured a holding facility for immigrants in Texas, highlighting what the Democrats say are inhumane conditions.

Lawmakers said they had been forced to give up their cell phones before being allowed into the facility - but Rep. Joaquin Castro (D-TX), whose brother is running for President - snuck a device inside, and snapped pictures and video of a group of women who spoke with members of Congress.

"Many said they had not bathed for 15 days. Some had been separated from children, some had been held for more than 50 days," Castro tweeted after the visit.

"Our border patrol system is broken. And part of the reason it stays broken is because it’s kept secret. The American people must see what is being carried out in their name," Castro added.

The visit also came after a ProPublica report about private Facebook groups which may have involved Border Patrol employees, who were making derogatory statements about immigrants and Democrats in Congress.

Hours after some Democrats had demanded an investigation, the internal watchdog of the Department of Homeland Security was asked to look into the Facebook posts.

"Now I’ve seen the inside of these facilities," said Rep. Alexandria Ocasio-Cortez (D-NY). "It’s not just the kids. It’s everyone. People drinking out of toilets, officers laughing in front of members Congress."

"The conditions are far worse than we ever could have imagined," said Rep. Madeleine Dean (D-PA), who called it a 'human rights crisis.'