Homeland Security triggered a waiver Tuesday allowing the department to bypass environmental and other land protection laws in order to begin building and testing President Trump’s new border wall. The waivers apply to San Diego, where officials already plan to upgrade miles of existing fence, but where they’ll also stage a competition this summer to build and test prototypes for Mr. Trump’s wall. It’s the first in what’s likely to be a series of waivers that will be needed as wall construction ramps up. Officials insisted they will still try to be mindful of local impacts as they work on...