Labor unions have been among the most vocal critics of Donald Trump and his expanding team of economic advisers, sounding warnings over the president-elect’s positions on a range of issues and promising to stymie his policy agenda when warranted.

Alas, federal data indicate the influence of labor unions — at least when it comes to membership — is waning. An analysis by the Bureau of Labor Statistics found that union membership as a percentage of the entire labor force declined in 24 states in 2015, while some 34 states and the District of Columbia were down from where they were a decade earlier.

States with some of the largest declines were concentrated in the U.S. Rust Belt. Wisconsin’s union membership as a percentage of its total labor force dropped 7.8 percentage points — from 16.1 percent in 2005 to 8.3 percent in 2015 — following a bitter policy battle that saw Gov. Scott Walker beat back rules around labor organizing and membership dues. Similar efforts in Indiana resulted in a 2.4 percentage-point slide, while Ohio (down 3.7 percentage points) and Michigan (5.3 percentage points) also ranked among the largest decliners.

Missouri’s concentration of union membership dropped 2.7 percentage points between 2005 and 2015, and now sits at 8.8 percent. But the decline of union membership in the state could increase in the near future, as Republicans have made passage of “right to work” legislation a priority now that the party controls the House, Senate and governor’s office. Right to work laws forbid union contracts that require workers to pay union dues as a condition of employment.

Despite its conservative reputation, Kansas had one of the largest increases in percentage of union members since 2005. In 2015, 8.7 percent of the state’s workforce were union members, up 1.7 percentage points from a decade earlier and up 1.3 percentage points from 2014. In raw numbers, Kansas had approximately 110,000 union members last year, compared with 95,000 in 2014.

New York, the state with the largest ratio of union members (24.7 percent) as a percentage of its total workforce, reported a 1.4 percentage point decline over the same decade. At 2.1 percent, South Carolina’s ratio of union membership ranked as the country’s lowest, having dropped by 0.2 percentage points between 2005 and 2015.

The longer-term trend is even gloomier for labor unions; membership as a percentage of the entire U.S. labor force fell to 11.1 percent in 2015, versus 20.1 percent in 1983. In total, the U.S. had 14.8 million union members in 2015, down 17 percent since 1983.

At the same time, the total number of wage and salary workers in the U.S. increased 54 percent to 133.7 million people, according to BLS.

Trump’s latest tangle with union members involved Chuck Jones, the head of United Steel Workers 1999. The incoming president recently unleashed a torrent of criticism and defensive jibes in response to accusations that he overstated the benefits from his negotiations to keep Indianapolis-based Carrier Corp. from relocating more than a thousand jobs from Indiana to Mexico. Trump aired most of his grievances via social media, calling Thomas’ representation of union members”terrible” and part of a broader labor agenda driving U.S. companies out of the country.

The back-and-forth came just weeks after a bare-knuckles election cycle that saw Trump repeatedly lock horns with labor leaders over a range of topics, from his support of charter schools to his practices as a real estate developer.

A Wall Street Journal analysis found that labor unions spent $110 million in support of political candidates in the recent election cycle. That was up 38 percent from the 2012 cycle, with the vast majority of that support going to Trump’s main opponent, Hillary Clinton, as well as other Democratic-party causes.

Craig M. Douglas

Director, Editorial Research & Analysis