I don’t know about that calculation. Trump’s base skews older in demographics. This is a demographic that is more vulnerable to COVID-19 than the overall population so I cannot imagine them being very happy about the crisis continuing for many months.
The absentee ballot situation is likely to change especially if things do not improve by the end of the summer.
First, it’s only 17 states where absentee ballots require an excuse, and out of those, only 6 (IN, LO, MS, SC, TN, TX) have age as a reason to get absentee ballot, still significant but “most” is definitely a bit misleading.
Second, outside of TX, all provide an excuse for being sick or disabled. Considering limitations on testing, I’d guess that a lot of people could claim to be sick. So that leaves TX - certainly a huge battleground - as the one that could see its absentee ballot laws challenged as voter suppression in case of a pandemic. Travis County Judge ruled in mid-April that fear of coronavirus would be a sufficient reason for voting by mail.
That has been mirrored in other states, in some like in Nebraska or New Hampshire, the Republican governors have already stated that absentee ballots rules will be expanded for the rest of the year.
This is only beginning though but a strategy based solely on voter suppression seems very risky to me, at least currently in the US. First, it could backfire and galvanize voters against your ticket if done too obviously. If GOP states are the only ones not to allow universal absentee ballot for this election, it is not good optics, no matter how many layers of voter fraud lipstick you can lather on this pig. Nevada judge ruled last month against blocking absentee ballot for all for primaries stating that there is no evidence that it would lead to increased voter fraud. I assume every state with restrictions on absentee ballots will see the same court battles well into the summer and early fall.
And even if it worked, it’d de-legitimize any elected incoming president beyond repair IMO. Trump was already elected while losing the popular vote by a significant margin. That’s not unique but not having a convincing popular mandate contributed to a very intense resistance throughout his term. I cannot imagine how bad it’d get if he got re-elected after mass voter suppression in up to 17 states. If something could precipitate the end of the Union, that could certainly do it.