"The state" refers to the governing apparatus, not a particular state within the union. I understand there may be some confusion if you are not familiar with the US government and typical ways of talking about it.
Please cite me where the power to enact a requirement to wear masks is explicitly granted to the federal government. I'll wait.
https://www.americanbar.org/news/abanews/publications/yourab...
Depends on the nature of the mandate. A simple hard mandate (everyone must wear masks in public or be subject individually to federal sanction) may not be authorized, but that's not the only shape of mask mandate possible.
A requirement that a state adopt and show adequate enforcement of control measures deemed necessary by the federal government, including (if deemed necessary) a mask mandate with given parameters or be subject to additional restrictions on interstate trade and travel to restrict the spread of disease to other states is absolutely not only within the scope of the Constitutional power of the federal government under the Commerce Clause, but also within statutory powers already granted to the executive branch under that Constitutional power, in the Public Health Services Act and elsewhere.
We need to start by recognizing that, although the Constitution is an important original source in understanding how our government functions, we have over 200 years of Constitutional interpretation that lies on top of it. You are welcome to make a Constitutional argument that goes against the existing jurisprudence, and Constitutional interpretation does change over time, but it does so only slowly. One of the most important principles in Constitutional interpretation is that of stari decisis, or issues which have already been decided. In almost all circumstances, courts adhere to precedence. This isn't always the case, but when you are fighting against the current understanding of the Constitution, you need to realize that you're fighting an uphill battle, and frame your arguments as such.
So where are we in our understanding of these issues? First, the Supreme Court has literally ruled that the Tenth Amendment is useless. Specifically, in US v Sprague (1931, SCOTUS ruled that the Tenth Amendment is a "truism" that "added nothing to the [Constitution] as originally ratified."[1] It was later used to create an anti-commandeering understanding, which in this circumstance just means that the federal government can't pass a law that requires states to enforce a federal mask mandate. There might be a public health exception to that though, but that's where the tenth amendment would be relevant.
You also need to understand that SCOTUS has repeatedly expanded the commerce clause to cover basically everything. The federal government can pass pretty much any law they want, say it affects interstate commerce, and win. You don't have to like that interpretation, but everyone follows it. It was only during the Rehnquist Court that a few exceptions were carved out, but they're very, very narrow. The most famous example was that the court ruled that the federal government couldn't ban handguns in schools under the commerce clause. But for anything even vaguely interstate, and a contagious virus certainly counts, the federal government is allowed to pass pretty much any law it wants.
The courts also tend to be pretty generous towards allowing emergency powers to deal with a genuine crisis. I expect that the federal government could do pretty much anything it wants to deal with COVID. I'm sure they'd allow a national lockdown by executive order right now. A legislative mask mandate would be completely non-controversial from a Constitutional perspective.
[1] https://en.wikipedia.org/wiki/Tenth_Amendment_to_the_United_... - Yes, this is Wikipedia, but I don't feel like reading a SCOTUS case to write a HN comment
When Trump was given his presidential megaphone he was able to convince a LOT of people to not wear masks by simply not wearing one and then telling people that's fine. At least by taking away the megaphone that's a step in the right direction. Even if there's no specific law that backs him up, that alone may save lives.
Second, even if technically not legal, presidential orders are OFTEN followed. It can be challenged in the courts for years but in the mean time, an order like that will probably have the effect of getting at least another 50M masks put on. That's a fucking win.
The other thing that is 100% legal, is the executive branch can restrict funding in specific ways if a state does not behave. If I was Biden, I would start there.