TPM:

I was talking to one midwestern Democrat about this. And this person told me they figured it was pretty likely Pennsylvania and Michigan would return to the Democratic fold in 2020. They were much less certain about Wisconsin. Indeed, they thought President Trump had a good shot at winning it.

Let’s set aside whether these prognostications are accurate. Let’s focus on the hypothetical.

When I pulled up my map I was surprised and dismayed to see the following.

If you take the 2016 election and re-add the number of electoral votes set aside by faithless electors you get Trump 306 and Clinton 232 electoral votes. (Presumably, though we can’t be certain, you don’t have faithless electors if they can really change the result.)

If you take combined 36 electoral votes of Michigan and Pennsylvania and remove them from the Trump column and reallocate them to the Democratic column you get a 268 to 270, an effective tie and an actual tie at 269 each if Democrats win both district electoral votes in Maine.
This assumes all the other blue or swing states stay in Trump’s column. One faithless elector makes it a tie. This is not at all an impossible scenario. The country would be ill-prepared in practice to manage a tie election in any circumstance. In present circumstances, the result could be very dark.