Looks like America supports the struggle. (Photo by Scott Olson/Getty Images)

As unions become a more forceful voice in the political discourse leading up to next year's elections -- both in their fierce opposition to the White House trade agenda and as a proposed solution to rising inequality -- it's important to know what the public thinks about them. We don't get that kind of data very often, but Pew Research just came out with a bunch of numbers that show a few important things: Opinions of unions have mostly recovered from a low point during the Detroit auto bailout, and strong majorities of people believe workers should be able to unionize across several different sectors.

Here's the graph of how positive and negative views of unions have changed over time:

They took a dive during the 2000s, and have since bounced back to where they were in the mid-1980s. The question that hasn't been asked before is whether people think workers should be able to unionize in certain industries. Pew found that people were overwhelmingly supportive of manufacturing workers unionizing, and least supportive of fast food workers unionizing -- perhaps because none of them have yet.

Of course, the question of whether people should be able to unionize isn't that applicable -- people in most workplaces are technically allowed to do so. The question is how hard it can be to make that happen. In fast food, for example, unions have found it essentially impossible to unionize franchised locations, since they're unable to bargain with the company that actually calls the important shots -- the franchisor. That's why they're trying to hard to get brands like McDonalds classified as "joint employers," which would make unionizing in fast food a less daunting proposition.

The final interesting bit here is about polarization, and its implications for politics. While opinions of unions overall have remained steady over the past few years, they've really diverged by party, with a large majority of Democrats thinking the decline of unions hurt workers very much and Republicans mostly thinking it benefited workers. People who strongly dislike unions also outnumber people who strongly approve of unions, 23 percent to 11 percent.

The opinion trends Pew identified could have mixed consequences. Those with extreme emotions are usually the most politically active, which means that super-engaged base could be more anti-union than not. But also, unions are also significantly more popular among people under age 30, people who make less than $30,000 a year, and black people rather than whites and Hispanics -- all relatively low-turnout groups. That could mean that unions might be a key actor in bringing them out to vote.