There’s no shortage of people telling Donald Trump he can’t build a wall on the U.S.-Mexico border. And maybe, in the end, he won’t do it. But at the moment Trump takes office, he will have the legal authority and the money he needs to get started on the wall. Yes, there will be obstacles — what’s the over/under on the number of lawsuits that will be filed trying to stop it? — but the fact is, the law is already in place that will allow Trump to go forward. As in other areas of immigration enforcement, Trump will be able to effect radical change simply by following the law. In this case, it is the Secure Fence Act, passed in 2006 with bipartisan support — 283 votes in the House and 80 in the Senate, including then-Sens. Barack Obama and Hillary Clinton. The law ordered the Secretary of Homeland Security, within 18 months of passage, to take all actions the secretary determines necessary and appropriate to achieve and maintain operational control over the entire international land and maritime borders of the United States.