Franklin Delano Roosevelt is probably rolling over in his grave. Union members are no longer the core of the Democratic Party. In fact, in six of the closest swing states, Donald Trump and Joe Biden are tied at 47% each among union members. In FDR's time, union members overwhelmingly voted for Democrats. This shift is why the northern swing states (see above) are trending purple. They used to form a blue wall. Wisconsin, Michigan and Pennsylvania voted for the Democrat in seven of the past eight presidential elections. Only in 2016 did the Republican (Donald Trump) win all three.
Until recently, union members voted largely based on kitchen-table economic issues. Abortion, gay rights, transgender rights, etc. played almost no role at all. If someone had told FDR that someday union members would care more about who plays on which high school sports team than how much they get in their pay envelope, he would have said the person who told him that was stark raving mad. As late as 1948, Harry Truman beat Thomas Dewey by 62 points among union members. But for many union members, money is apparently not a problem anymore, so they have the luxury of voting their cultural attitudes.
Unions are especially strong in Michigan and Pennsylvania, but also in Nevada (the culinary union). But not all unions are the same. Biden is making a strong effort to win over UAW members, but Trump is going after members of the Teamsters Union.
When trying to understand what is going on, remember that unions have changed. In FDR's day, the typical union member worked on an assembly line in a factory. Now many more union members are in the public sector than in the private sector, and in services rather than in manufacturing. The five biggest unions are the National Education Association (3 million members, largely teachers), Service Employees International Union (1.9M), American Federation of State, County, and Municipal Employees (1.5M), Teamsters (1.4M) and United Food and Commercial Workers (1.3M). Only when we get to #6, the UAW (1M), do we hit assembly line workers.
Another factor to keep in mind is that not all assembly line workers are unionized. Many of the new car factories created by Japanese, South Korean, German and other foreign car makers are in states in the South and are nonunion shops. Nevertheless, the people who work there usually respond the same way to the candidates as union members. (V)