Donald Trump took his bid to end birthright citizenship to the US Supreme Court on Thursday, in a case that could help further his agenda on immigration and other issues.
The case asks whether lower court judges should be able to block presidential orders for the entire country, as they have done in this case.
The justices did not appear to reach a consensus, as they considered both sides.
The US solicitor general argued that lower courts overstepped their authorities, saying the power should be curtailed.
Meanwhile, the New Jersey solicitor general, arguing on behalf of a group of states, said siding with Mr. Trump would create a patchwork system of citizenship.
It is not clear when the court will issue its decision.
If it agrees with President Trump, then it could continue his wide-ranging use of a executive orders to make good and campaign promises without having to wait for congressional approval with limited checks by the courts.