WASHINGTON (AP) - House Speaker Paul Ryan says President Donald Trump can't end birthright citizenship on his own.

  

The top Republican tells WVLK radio in Kentucky, "Well you obviously cannot do that. You cannot end birthright citizenship with an executive order."

  

Ryan's comments Tuesday offered a rare challenge to the president - from his own party.

  

Trump tells "Axios on HBO" he wants to end birthright citizenship for babies born to non-citizens and immigrants not authorized to be in the United States.

  

Constitutional scholars are questioning whether changes could be made without Congress.

  

Ryan says Republicans didn't like when then-President Barack Obama "tried changing immigration laws via executive action. He says "obviously as conservatives we believe in the Constitution."

  

Ryan is retiring but the No. 3 House Republican, Louisiana's Rep. Steve Scalise, said on Fox that he's glad Trump is considering options.