Sun Belt vs. Rust Belt

[ShamDam]

In thinking about the Democrats' electoral strategy for 2020, I see the two main paths to victory being either reclaiming the Rust Belt, which is trending away from Democrats but was only barely lost in 2016, or finally making the necessary inroads in the Sun Belt, which has states we lost by 3-9 points but that seem to be trending towards us.

I'm worried that by 2020, neither strategy will be ideal. If Michigan/Wisconsin/Pennsylvania start to behave electorally more like Iowa and Ohio, but Arizona/Georgia/Florida are still JUST out of reach (with perhaps even Texas being within 5 points) I could see Democrats losing despite gaining even more of the popular vote because we lose like 7 or so states by 5 points or less.

What say you? If you were strategizing for the electoral college, which states would you be inclined to focus on? Or should we just worry about presenting a message that broadly appeals to voters in any of those states?

[ShamDam]

Or should we just worry about presenting a message that broadly appeals to voters in any of those states?

This is the only non-"Dover Beach" answer.

Excellent analogy. Correct as well.

What does it mean to be a "Dover Beach" answer?

[ShamDam]

Or should we just worry about presenting a message that broadly appeals to voters in any of those states?

This is the only non-"Dover Beach" answer.

Excellent analogy. Correct as well.

What does it mean to be a "Dover Beach" answer?

Have you heard of the Dover Cliffs?

I hadn't! I've Googled so now I have, but I'm still not seeing the connection.