Limitations on ammo importation have indeed cramped the supply chain. To what extent, it's very difficult to say, as this really only affects finished cartridges that are considered armor-piercing, which obviously includes some fan favorites such as mil-surp 5.45x39 and 7.62x39, and potentially anything else with a steel core. But if you had, say, a hypothetical lot of lead-core ammo sitting offshore, file the paperwork and bring it in. The fact of the matter is that this hypothetical lot - and more importantly, the surplus industrial capacity to produce it - largely does not exist. Same for the components required to produce it.
Domestically, regulation may be a PITA for anyone wishing to manufacture ammo (or anything else, for that matter), but it's a red herring. If you've got the monetary capital to invest in the physical capital to manufacture ammo in high volume, it's just overhead. The bigger issue is that no one wants to invest in the physical capital just to accommodate a short-term need, and then watch the bottom fall out of the market when Trump wins and demand evaporates, or Biden wins and bans everything. I'm not privy to the financial records of ammo manufacturers, but I bet the 2-3 years running up to March of 2020 really sucked, and it's quite possible that by the time a new line is up and running by sometime in 2021, it's gonna be back to stacks of pallets in the aisles of Cabela's.
Oh, but this time, it's different. Yep - pretty sure that the CPAs at ammo and component manufacturers have heard that line again. And maybe it is different this time, and if that's the case, then the demand will still exist after the election and capital can be allocated properly. Otherwise, all the "smart money" is getting dumped into markets with better returns (like Apple and Tesla stock) where it's possible to make money with far less work (and much quicker returns) than making an actual product.
I honestly don't think the situation changes until the Trump adminstration does something similar to what was done with Kodak - invoke the Defense Production Act, and provide monetary capital at a low cost. And then that would just introduce distortions in the market that would have other unintended consequences, and then we're back to bitching about something else.