We lost but we shouldn't totally panic [View all]
First, in my lifetime we have lost way worse than this several times. In 1972 we lost 49 states and by 20 points. In 1980 we lost 44 states and by 10. In 1984 we lost 49 states and by 19 points. In 1988 we lost 40 states and lost by 7. Those were real losses that necessitated vast changes in strategy to recover from. This loss wasn't that. We were an incumbent party at a time that being one was a bad idea. In comparison to incumbents in nearly every other country, our loss was minimal.
In short, we don't need a complete rebuild. At least not for the President. The fact is for President, I think we should be at least slight favorites in 4 years all things being equal.
Our real structural problem is the Senate. We have no seats in states carried by Trump all three times. Those states have 50 seats. If take out NC, which was competitive all three times, that falls to 48. Currently that makes our ceiling for the Senate 52 seats unless we find a way to win seats in states we aren't competitive in for President. That is the problem we need to solve. It wasn't that long ago, that we had Senators in states we had no real prayer of winning at the Presidential level. We held all four of the Dakota seats for several years despite not winning those states at the Presidential level in my lifetime.
We need to figure out how to win some of these seats. We can't depend on running the table in every possible state to get to a bare majority. Again, we actually nearly ran the table in those seats to get where we are now. The only seats we don't have in those states are Collins in ME, McCormack in PA, Johnson in WI, and both NC seats. Going forward we need to find states we can win Senate seats in and target them. Preferably reasonably cheap ones. My suggestions would be Kansas, Alaska, Montana (a Tester comeback), and maybe Nebraska. That is some thin gruel but it has to start somewhere.