Washington (CNN) President Donald Trump on Wednesday said he is "seriously" considering ending US birthright citizenship despite the fact that such a move would face immediate legal challenge and is at odds with Supreme Court precedent.

"We're looking at that very seriously, birthright citizenship," Trump told reporters outside the White House, echoing his administration's previous vow to unilaterally end the process by which babies born in the country automatically become citizens.

The President did not elaborate on what he meant.

Trump's statement came as the administration announced a proposal to detain undocumented families together indefinitely, replacing the agreement that set a 20-day limit for holding children.

The 14th Amendment of the Constitution guarantees birthright citizenship and states: "All persons born or naturalized in the United States and subject to the jurisdiction thereof, are citizens of the United States and of the State wherein they reside." The ability of a president to end birthright citizenship has been extensively challenged by a range of lawmakers and legal scholars -- including one of Trump's own judicial nominees.

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