Expert says legal battles ahead for Trump's 'unprecedented' move A legal expert says Donald Trump's declaration of an emergency to build a border wall will draw legal challenges from both states and individuals, calling the move "unprecedented." William Yeatman, a research fellow at the CATO Institute in Washington, says when it comes to questions over presidential power, the courts "take a very hands-off approach", but also says there is a "very strong" argument that the action violates the Constitution. IMAGES AND SOUNDBITES