The main swing states fall into two groups. Some people talk about the Rust Belt vs. the Sun Belt. People who talk this way are often from the Sun Belt. More neutral names are "the northern route" and "the southern route." The northern route states are clustered around the Great Lakes: Wisconsin, Michigan, and Pennsylvania. They used to be dominated by heavy industry. The southern route states are Nevada, Arizona, Georgia, and North Carolina. They have almost no heavy industry. Interestingly enough, the northern states used to be solidly blue until Donald Trump came along. Since then, they have become purple. The southern states were mostly red for years until Barack Obama and Joe Biden came along. Since then they have become purple.
What changed is that until Trump, blue-collar workers in the northern states were largely Democrats on account of economic issues. In 2016, he peeled off many of them on account of cultural issues. In the South, the Democrats are now doing better than in the past due to an increase in Black and Latino voters.
A key question for the Biden campaign is this: Do they want to pursue formerly blue states that are going red or formerly red states that are going blue? The campaign could split the money and appearances 50-50, but that could risk doing a bad job in both regions. If Biden wins either set of states and loses the entire other set, he still wins, as long as he can hold all the states in either group that he won in 2020.
Decisions of where to advertise and where to campaign are made by campaign strategists based on (ever-changing) polling and long experience. Pundits also have plenty of opinions on which route to take. Harry Enten at CNN has looked at the current polling and believes that (at the moment) the northern route looks more promising for Biden. Biden has led in every serious poll this cycle in Wisconsin. Pennsylvania has been mixed. Michigan has been the worst of the three, although better than any of the swing states in the South. Part of Biden's Michigan problem has been the Arab-American voters around Dearborn. But Biden could counter that by making sure everyone in the area knows Trump's views on the Middle East.
What's also noteworthy here is that in the polls, Biden does better among likely voters than among registered voters. The likely voter screens aren't very good this early in the cycle, but suggest that a fair number of the Trump supporters like grousing but not voting.
Biden won Nevada, Arizona, and Georgia in 2020, although he lost North Carolina by about 1 point. Why is he doing worse in all of them this time? Part of it is due to his much-reported losses among Black and Latino voters, who constitute a much larger fraction of the electorate in the South than in, say, Wisconsin. In Wisconsin, Michigan, and Pennsylvania, 80% of the voters are white. In the southern swing states, that is 70%. Problems with Black and Latino voters don't hit as hard in states with fewer minority voters.
Biden is well aware of his weakness with Black and Latino voters (actually, Black and Latino men, not women). Trump's macho personality appeals to these men. Biden is not macho so he has to find some other way to appeal to them. Emphasizing the good economy and the fact that anyone looking for a job can find one now is certainly one way and he will no doubt talk about this a lot. (V)