Natalie Sherman
New York business reporter

The past four years have seen an increase in union organizing, public support for unions, and strike activity in the United States.

The latest example is Boeing, where factory workers rejected the company's wage offer for the second time on Wednesday, further extending the strike.

In theory, the rise of labor could bode well for Democrats, who have long viewed unions as an important part of their base and supported issues like stronger worker protections that are among workers' top priorities.

But since Donald Trump has made appeals to the union base a key part of his campaign, that hasn't happened.

Kamala Harris and Tim Walz have received the support of major organizations such as the United Autoworkers, the AFL-CIO and the Boeing Machinists.

But other major unions, such as the Teamsters, have withheld their endorsement at the national level, a sign of fierce internal divisions among their members over the candidates.

This divide is particularly clear in swing states like Michigan and Pennsylvania. For example, although the leadership of the U.S. Steelworkers union supported Harris, Trump held rallies in Pennsylvania to highlight the support he receives from local union members.