Unfortunately, but not surprisingly, Whitmer fails to provide any constitutional justification for such a mandate. I know it sounds quaint to a Democrat or, for that matter, to a Republican, to bring up the Constitution in the midst of a crisis, but it's important that we libertarians continue to call these people out when they endorse tyrannical measures, especially since it might dissuade them from endorsing even more.
When the delegates at the Constitutional Convention proposed replacing the federal government under the Articles of Confederation with a new federal government under the Constitution, the American people were leery. They didn't want a federal government that wielded the power to do the "right" thing, even in crises or emergencies. They knew that that was a surefire way to lose their liberty and their well-being.
No problem, the proponents of the Constitution responded. By the terms of the Constitution itself, which was the document calling the federal government into existence, its powers would be limited to those enumerated in the document. If a power wasn't enumerated, it couldn't be exercised.