Regarding NB drifting to the left: it’s interesting that few states actually moved to the left over the past decade. AZ, GA, NH, CO, VA, TX and potentially NB and MS. In the latter, nearly 40% of the voters are African Americans/ blacks. That’s surely a state to watch in the future (not 2024 or 2028).
What the Dems should do is to put back FL and OH in play. Luckily, neither was a blue state: Obama won them twice, but so did Bush. In other words, no traditionally blue state has become red, while some traditionally red states became purple or slightly blue.
Democrats can really expand their map by the end of the decade and the beginning of the next. A relatively conservative Democrat, a la Clinton, can help with that.