I know the red/blue model is useful in some cases but I live in a red state (Louisiana) in one of the most blue cities in America (New Orleans). Biden won like 40% of the statewide vote and we have a two-term Democratic governor (about to leave office but still). And that’s with a state Democratic Party that is a constant mess, never has resources, gets zero national investment or attention, and sometimes doesn’t even field candidates.
National politics isn’t everything. Sure, Biden shouldn’t spend much time or money here but Democrats have no excuse not to have an aggressive 50 state operation. Just having a credible candidate means a scandal can flip a Congressional seat but attorney generals and secretaries of state matter too. There’s even value in losing an election even if your candidate is just on the local news calling out his opponent.