In a series of tweets fired off on Sunday, US President Donald Trump described people entering the country from Mexico as "invaders" trying to "break into the country," and suggested sending them back to their country of origin without legal proceedings.

"When somebody comes in, we must immediately, with no Judges or Court Cases, bring them back from where they came," he wrote.

American civil rights advocates immediately responded that such a procedure would violate the US Constitution.

"What President Trump has suggested here is both illegal and unconstitutional," a tweet from the American Civil Liberties Union (ACLU) read. "Any official who has sworn an oath to uphold the Constitution and laws should disavow it unequivocally."

The White House fired back at such criticism during the regular White House press briefing on Monday. Administration spokeswoman Sarah Sanders said that barring undocumented immigrants from seeing a judge would not be a violation of due process.

"Thousands of illegal aliens are removed every month without seeing an immigration judge as a result of procedures in current law, including voluntary removal and expedited removal," she told reporters.

She added that, "Virtually all Americans agree that it makes no sense that an illegal alien sets one foot on American soil" and then goes through a multi-year legal deportation process.

Raising ethical eyebrows

Trump's tweets were the latest to display his hardline stance on immigration, a core part of White House policy that has increasingly raised ethical concerns from Democratic and even some Republican lawmakers recently.

Trump gave in to bi-partisan pressure last week and reversed a policy that ordered the separation of children from their parents who enter the US unlawfully. However, his "zero-tolerance" policy of criminally prosecuting all undocumented border-crossers remains in place.

Read more: Trump's migrant family separations reversal too little, too late

On Saturday, the Department of Homeland Security released its first data on family separations since Trump changed the policy. Some 500 children have been reunited with their parents, the data said, but more than 2,000 continue to be held separately by government officials.

Congress is set to vote on two Republican-backed immigration bills this coming week. Trump has sent mixed messages about the attempts to reform immigration policy before midterm elections in November.

Read more: Opinion: If family separation isn't enough, what must Trump do to cross Republicans?

Strong crackdown for a strong US

Trump has been consistent, however, in using rhetoric that blanket categorizes undocumented immigrants as dangerous and violent criminals. He has also painted his crackdown on immigration as a way to regain American strength and stature on the global stage, in line with his "Make America Great Again" slogan.

"Our Immigration policy, laughed at all over the world, is very unfair to all of those people who have gone through the system legally," he said in one of his immigration tweets on Sunday. Most people arriving at the US border immediately request asylum.

People in cities across the US protest Trump's policy of separately detaining refugee children from their families

Trump's stated goal of making the US strong has been marked by isolationist moves, such as withdrawing from the UN Human Rights Council, as well as by warm overtures to authoritarian leaders such as newly re-elected Turkish President Recep Tayyip Erdogan.

Migration a global topic

Trump's tweets on immigration came the same day that European leaders including German Chancellor Angela Merkel gathered for an emergency meeting in Brussels on migration.

Trump has repeatedly criticized Merkel for her immigration policy, and used Germany as an example of the dangers of migration, including one factually inaccurate claim about crime and immigration.

cmb/msh (AP, AFP)

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