So here's my take with my colleague John Halpin, just out on the Prospect website. Below is the intro to the article. Read the whole thing for some detailed exploration of Democrats' chances in GA, AZ and TX in particular.
"Any realistic assessment of President Trump’s geographic and demographic strengths leads to the conclusion that Democrats need to focus first and foremost on Trump’s backstop of white working class voters in the upper Midwest—particularly, the trio of Pennsylvania, Michigan, and Wisconsin that, along with Florida, tipped the Electoral College in his favor in 2016. Trump is a deeply unpopular president nationally, but he retains a hold on many voters in these states. Any Democrat hoping to pull off the difficult task of unseating an incumbent president—even one as divisive as Trump—must be able to mobilize base Democratic voters and cut into his margins with white non-college educated voters in these trio of states.
Alternative strategies have been floated, contending that Democrats can essentially ignore these states and these voters and instead turn to a coalition of voters of color and white liberals in emerging battlegrounds in the south and Sunbelt regions. Although these emerging voting blocs are essential parts of the Democratic coalition, this advice makes little sense strategically. It would be irresponsible for the eventual nominee to concentrate resources in states that Democrats have not won in recent presidential elections only to ignore states like Pennsylvania, Michigan, and Wisconsin (plus Florida) that Barack Obama successfully captured both times he stood for president.
But Democrats at this point should know how to walk and chew gum at the same time, particularly with the chance to recapture both the presidency and the U.S. Senate. The party and its eventual nominee will almost certainly raise more than $1 billion in the upcoming cycle, and with campaigning already beginning, nearly two years before the actual 2020 election, Democrats have the time and the resources also to expand the map beyond those four key states and thereby stretch Trump thin in 2020."