It was a historic moment when President Joe Biden became the first sitting president to join a picket line. Members of the United Auto Workers are taking part in targeted strikes at plants for the Big Three US automakers. Biden joined the picket line at a General Motors facility in Van Buren Township, Michigan, appearing alongside UAW President Shawn Fain. There’s a reason presidents don’t usually walk picket lines, according to Timothy Naftali, former director of the Richard Nixon Presidential Library. “Presidents have basically positioned themselves as mediators between both labor and management,” Naftali said Tuesday on CNN, although he noted that Democrats generally lean in their sympathies toward labor while Republicans lean toward management. The general election is starting before the primary ends Former President Donald Trump also wants to claim some support among union members. He will appear in Michigan on Wednesday, although at a non-union facility and without any official sanction by the United Auto Workers. He will carry a message to undercut Biden’s sympathy for better union contracts. Trump and Republicans argue that Biden’s push for electric vehicles with taxpayer credits puts union auto jobs at risk and is “stabbing” autoworkers in the back. EVs cut down on carbon emissions to help the environment. They also require fewer jobs for assembly. The former UAW president Bob King said on CNN on Tuesday that voters should look to Trump’s four years in office to gauge his support for workers. “There’s a long, long list of ways that he helped the wealthiest and did not help workers at all,” said King. Biden, meanwhile, has argued the autoworkers helped save the auto industry by accepting worse contracts during the Great Recession and now they should get more from Detroit. The UAW has not endorsed Biden’s reelection campaign, although that seems like an ultimate foregone conclusion. Trump, meanwhile, won’t have to win union workers in order to win a state like Michigan. Simply eating into Biden’s margins could do the trick. So, it’s no coincidence that union household voters are the subject of this very public contrast between Trump and Biden. “I really think it’s the opening salvo of the presidential campaign,” said the historian Douglas Brinkley, appearing on CNN on Tuesday. While you’re going to read a lot about the future and new technologies like artificial intelligence, Brinkley said the coming election “well might be about the Midwest working class union workers and how they vote.” Biden and Trump, Brinkley said, “both understand that.” Unions are key in key states Fewer and fewer Americans are members of a union, but they play a continually important role in US politics. Biden won the White House by rebuilding Democrats’ blue wall of support in heavily unionized Rust Belt states. But it’s important to note that Republicans don’t need to win union households in order to win elections. When Trump won the blue wall state of Michigan in 2016, he got the support of 40% of union households, compared with Hillary Clinton’s 53%. But when Biden won Michigan in 2020, he got the support of 62% of union households and Trump was under 40%. The shift was similar in Wisconsin. The national picture The share of voters nationwide who reported being in a union household in those 2020 exit polls was at 20%, and they went 56% for Biden to 40% for Trump. When Trump won in 2016, 18% of voters reported being in a union household, and they were more evenly split between Clinton, 51%, and Trump, 42%. Fewer union households In years where Republicans have done particularly well, the union vote has been split. Richard Nixon actually won 50% of voters in union households for his 1972 romp over George McGovern, the only presidential election in the past 50 years in which a Republican won more votes from union households than the Democrat. Ronald Reagan got 44% of union household voters in his 1980 landslide. A more gradual and persistent trend is the shrinking portion of voters who report living in a union household. About a third of voters lived in a union household in the 1970s. That fell to under a quarter by the 1990s. It’s been at or under 20% since 2010. Restriction on organizing In the intervening years, a multitude of states enacted so-called “right-to-work” legislation making it more difficult for unions to organize by giving workers the option to opt out of a union even when their job is covered by a collective bargaining agreement. This is a trend that extended to blue wall states like Wisconsin and Michigan, although Michigan repealed its “right-to-work” law this year. A resurgent approval of unions Paradoxically, while fewer Americans belong to a labor union, unions are having a long-term rebound in popularity in recent years. Asked simply if they approve or disapprove of labor unions, more than two-thirds of Americans said they approve in the most recent Gallup poll. That’s up from fewer than half in 2009, but still short of the more than 70% approval unions enjoyed in the middle part of the 20th century, according to Gallup. And the most pro-union president is? Biden is not the first union-friendly president, or maybe even the most pro-union, although the White House wants to claim that mantle for Biden. Franklin D. Roosevelt wove labor-friendly legislation into the New Deal and oversaw a massive uptick in union membership. For much of earlier US history, presidents were known more for antagonizing unions than joining them – helping companies and owners put down strikes, including with help from the US military, as when Grover Cleveland dispatched troops to put down the Pullman strike in 1894. The Republican Theodore Roosevelt broke this trend when he helped broker an end to a massive coal worker strike in 1902. Why take sides? Naftali argued Biden is willing to break the norm of the president being viewed as a mediator and instead take public sides. “Joe Biden knows that to be a second-term president he has to hold his base and part of that base is union America,” Naftali said, adding that Biden will be willing to take more chances to keep Trump from the White House. Biden will need to find an answer to Trump’s argument about EVs and the skepticism they create among autoworkers. Bringing the labor movement he has long supported into alignment with the environmental movement could be a key to Biden winning a second term.