Labor unions play a central role in the Democratic party coalition, providing candidates with voters, volunteers, and contributions, as well as lobbying policymakers. Has the sustained decline of organized labor hurt Democrats in elections and shifted public policy? We use the enactment of right-to-work laws--which weaken unions by removing agency shop protections-- to estimate the effect of unions on politics from 1980 to 2016. Comparing counties on either side of a state and right-to-work border to causally identify the effects of the state laws, we find that right-to-work laws reduce Democratic Presidential vote shares by 3.5 percentage points. We find similar effects in US Senate, US House, and Gubernatorial races, as well as on state legislative control. Turnout is also 2 to 3 percentage points lower in right-to-work counties after those laws pass. We next explore the mechanisms behind these effects, finding that right-to-work laws dampen organized labor campaign contributions to Democrats and that potential Democratic voters are less likely to be contacted to vote in right-to-work states. The weakening of unions also has large downstream effects both on who runs for office and on state legislative policy. Fewer working class candidates serve in state legislatures and Congress, and state policy moves in a more conservative direction following the passage of right-to-work laws.
Many people who oppose, and many people who support, right-to-work laws think the following: because such laws weaken unions' power to use employees' dues to contribute to political campaigns,right to work laws will cause there to be fewer union contributions to Democratic candidates than otherwise. It turns out that both sides are right. Feigenbaum et al find, as the abstract above says, that union contributions are lower than otherwise in such states and that this makes the vote for Democratic politicians lower than otherwise.
The ideal libertarian solution to the issue of unions is not right to work laws; the ideal solution is freedom of association for employees and employers. People should be free to join unions or not, and people should be free to work for employers who require unions, for employers who don't require unions, and for employers who refuse to deal with unions. The freedom of association applies to employers as well as employees. That means that if some employers want a requirement that every employee be a member of a union or, if not a member, be required to pay dues to a union, this should be allowed. Right to work laws prevent this. However, the number of employers in this category is likely to be very small. So right to work laws are a substantial step toward freedom of association.