The independent Government Accountability Office has served Congress as the nation’s chief investigator of wrongdoing at federal agencies for more than a century. Now it’s under assault. The typically uncontroversial, under-the-radar agency is fighting to retain power against attempts by Republicans in the Trump administration and on Capitol Hill to undercut its legal conclusions and independence — an onslaught that has been fast and furious. First, Elon Musk’s Department of Government...