Mr. Trump said they should be deported with "no Judges or Court Cases".
Last week, the president found himself on the defensive over his hard-line immigration stance, signing an executive order Wednesday reversing his family separation policy that instead seeks to detain children with their families.
In another tweet, Trump said, "Our immigration policy, laughed at all over the world, is very unfair to all of those people who have gone through the system legally and are waiting on line for years!"
His tough comments come after he was forced to back down on his zero-tolerance approach to migrant children.
It was another twist in an already head-spinning series of developments on immigration after the president reversed a policy last week that had resulted in the separation of more than 2,300 children from their families. Leonard Lance, R-7th Dist., and Brendan Boyle, D-Pa., to propose legislation requiring the administration to reunite the families.
But despite issuing his executive order, Trump has maintained that his "zero tolerance" policy, introduced by Attorney General Jeff Sessions in April, will remain. No Democrats voted for the bill, while 41 Republican voted "yes".
White House representatives did not immediately respond to HuffPost's requests for clarification on Trump's tweets and who precisely he meant in referring to "these people". "We need people to come in but they need to love this country to help make America great again".
The US Constitution's Fifth Amendment guarantees the right to "due process of law" in criminal proceedings.
"We believe "expedited removal" fails to afford a meaningful opportunity to defend oneself, and that, whatever its validity when employed at the border, it would be unconstitutional as applied to those living among us who are entitled to full due process protection", David D. Cole, national legal director for the American Civil Liberties Union, told the Los Angeles Times in March 2017.
Trump has been criticizing immigration judges for weeks, both exaggerating the number now hearing cases and saying that hiring more - as some members of Congress have proposed - would be unnecessary. "The president's suggestion that there is a ton of process for these individuals is simply wrong. Strong Borders, No Crime!"
"We are the only people, people walk in and put a foot in, 'Please, would you like to register?' Other countries say get the hell out of here".
One of the protesters, Martha Garcia Mercado, said: "Those are my kids in there and I want them to know we're fighting for them".
"Here, I think he is making it clear, he just doesn't want anybody here".