Customers shopping in the deli isle at WalMart Stores Inc. in Rogers, Ark., in 2008. (AP Photo/April L. Brown)

The term "middle class" is a funny thing in politics. It doesn't have an exact definition -- no minimum or maximum salary limits, no requirements to own a home that's nice but not too nice -- but it's used constantly, and for that exact reason. Almost everyone is America considers themselves middle class.

According to Pew, 87 percent describe themselves as either "middle class," "upper-middle class," or "lower-middle class." So it's no wonder politicians love the term. When they use it, about nine out of 10 Americans think the politician is talking about them.

(via Pew)
(via Pew)

If you think of class identity as how people feel the stress of money, it makes sense most people feel middle class. Being middle class can mean being able to pay your bills, but feeling like you could stand to earn a little more. A little more for savings, a little more to pay down debt, a little more for emergencies, a little more disposable income. It's about the limit to how much you can get ahead, how much of your paycheck you don't have to pay your bills with.

Or how much of an unexpected expense you could afford to pay for. These numbers, of course, differ for everyone. But for nearly half the U.S., $400 is too much. According to a Federal Reserve report, 47 percent of respondents said they either wouldn't be able to cover an unexpected $400 expense through savings or their credit card or would have to cover it by selling something or borrowing money. The statistic was first noted by AllGov.

Here is how that looks across income levels and race. This chart looks at the percentage who say they would be able to cover such an expense.

Those who make less than $40,000 are the most likely to have a problem with an unexpected $400 expense, especially if they are black or Hispanic (which are the income and race demographics that are also the most likely to self-identify as "lower class"). But perhaps most surprising is more than a quarter of people who make more than $100,000 say they would have the same problem -- including more than four in 10 blacks and Latinos.

It's further proof of why the self-identified middle class is so large and why it's such useful shorthand in politics. (It's also proof that maybe you should put away a little extra this month. You never know when you're going to need an extra $400, no matter where in the middle class you self-identify.) People who consider themselves "lower class" are having a hard time getting ahead, but people making six figures can feel the same way.

Talking about the struggles of the middle class, it turns out, casts a wider net than you might think.