The U.S. government has officially entered a shutdown, bringing with it the rising threat of mass federal layoffs and cuts to safety-net programs. In the final hours before funding lapsed, President Donald Trump escalated the stakes, warning that the administration might exploit the shutdown to enact “irreversible” cuts to health care and social benefit programs. “We can do things during the shutdown that are irreversible, that are bad for them,” Trump told reporters on Tuesday, referring to...