Unions have been a Democratic stronghold, with candidates from the party being able to rely on endorsements from the labor groups in key races, but with the shifting Republican Party under former President Donald Trump, the GOP has put a dent in the inevitability of unions supporting Democrats.

The most notable shift in union support for Republicans came last week when the International Brotherhood of Teamsters declined to endorse a candidate in the presidential election, marking the first non-endorsement by the union since 1996. The last time the Teamsters supported a Republican candidate for president was 1988, but like other unions, the Teamsters had widely been seen as a shoo-in endorsement for Democrats in recent decades.