Source: Bureau of Labor Statistics June 2015 Employment Situation Report
Source: Bureau of Labor Statistics June 2015 Employment Situation Report

Last week, Jeb Bush seemed to suggest people need to work longer hours in order to improve the economy. He later said he was talking only about part-time employees. But Democrats have pounced, believing Bush's "work longer hours" comment is their ticket to winning over middle-class voters.

And the Democrats' case is easy to make. Worker productivity -- what employers get for what they pay -- has been growing since the 1970s, while incomes for the majority of Americans have not. So, for Democrats, even the possibility that the millionaire scion of a premier political family had suggested that people need to work more was, shall we say, an animating event.

Whether you think the Democrats' attack is fair or not -- and our colleagues at Wonkblog parsed Bush's argument pretty deeply -- there is a real question at hand. And that is just how many part-time and unemployed American workers would like to work more hours? Who are they and why don't they simply do it?

First let's set the stage. Here's what employment looks like in the United States.

In June, nearly 63 percent of individuals over the age of 16 who were interested in working were either doing so or were hunting for a job. You might have heard this figure pop up when the jobs report does; it's known as the "labor-force participation rate," and it's used by skeptics of the Obama economic recovery to argue that many people have simply given up trying to find a job, and that this has superficially improved the unemployment rate (which tracks only those actively seeking work).

Anyhow. It's a figure that's been declining since 2007. And it's a figure that still hasn't returned to pre-recession levels. Economists watch the labor-force participation rate closely because it's seen as an indicator of bigger and important trends such as how much of the population has aged out of the workforce, the matchup between worker skills and jobs and how the costs of working such as childcare and commuting compare to earnings.

Take a look at these projections released by the St. Louis Fed.

Source: St. Louis Fed analysis of Bureau of Labor Statistics data
Source: St. Louis Fed analysis of Bureau of Labor Statistics data

The share of men working has been in decline since the 1970s. But for women, labor-force participation climbed during much of that same period until something changed in recent years. Some think it’s the difficulty of balancing work responsibilities and costs with family needs.

Source: Pew Research Center

So does that mean that all these workers could just elect to go back to working full-time?

A lot of them are at home caring for children, other relatives or have returned to school or taken on other tasks important to their families. In October 2014, government data-gatherers found that one of those things was true about a little more than 93 percent of adults not in the labor force.

OK. So most of those folks are out. What about folks working part time?

Well, seasonally adjusted federal data indicates that nearly 27 million people worked part-time in June. That was about 18 percent of the labor force last month. And since the same number of people who were working part-time a year ago, there are no signs this group is growing. But that figure does remain elevated when compared to the years before the recession.

Of course, some of these workers are teenagers. ( See Table 1 here. There were 4.1 million of them on average each  month in 2014.) If they rank among the lucky few who found summer and after-school jobs, they really might not want or be available to work any additional hours.

But the vast majority -- about 20.4 million part-time workers -- told Labor Department researchers they worked part-time in June for those same "non-economic reasons" mentioned above. In other words, they have other responsibilities that demand their time.

Then consider the number of people already working a lot.

Many workers not currently eligible for overtime pay are already putting in more than a full-time week. That's something the Obama administration is trying to fix by expanding overtime eligibility. And the average American full-time employee already puts in an average of 47 hours each week.

So back to those folks with part-time jobs. About 7.5 million people actually work full- and part-time jobs in some combination. A very small share of that group, 1.8 million people, have two part-time jobs. That figure dropped a little in the last year. But since these workers are concentrated in low-pay industries, some of them would really prefer single full-time job. Still, if they found one, this may not actually translate to more hours than they work right now.

Source: Bureau of Labor Statistics

So who really could work more hours?

For now, this is what we know for sure.

About 6.1 million people worked part-time in June because their employer cut their hours or because the only jobs they could find were part-time gigs. These people would ostensibly, in most cases, like to work more. There were about 8.3 million people who were unemployed and another 1.9 million people that the Labor Department considers only marginally attached to the workforce because they haven't looked for work recently.

So, perhaps this whole group, about 16.3 million people --  10.3 percent of the American labor force in June -- could work more hours, as Bush suggests. That's if they could find an employer who wants and needs them.

Think of them like this slice of the labor-force pie.

Source: Bureau of Labor Statistics, June Employment Situation Report
Source: Bureau of Labor Statistics, June 2015 Employment Situation Report