For several years now, two colleagues and I have been interviewing white working-class voters in the Midwest about their political beliefs. Our interviews suggest a strategy for defeating Donald Trump.

The biggest surprise was what the word “conservative” means to these voters. Before we conducted this study, we thought the word “conservative” referred to a worldview that favors traditional attitudes and behavior, and opposes social change. In economic terms, we thought “conservative” meant lower taxes and less regulation.

But that’s not what the self-identified conservatives among our interviewees believe. Over and over again, they told us that “conservative” means paying one’s bills and staying out of debt. We were surprised by the strength of the passion expressed on this point. For our respondents, a conservative is someone who is frugal and avoids debt. A liberal, by contrast, borrows and goes into debt.

Our interviewees associate these patterns with conservatives and liberals at both the individual and governmental level, and they vote for Republicans because Republicans are more likely to talk about avoiding debt as a moral issue for individual families and for the country.

In the words of one interviewee, “Democrats are liberal. I’m conservative so that has a bearing on my thinking. I was always taught if you don’t have the dollar, you don’t buy. Look at the trillions that our government is in debt, our nation, and they continue to spend, spend, spend.”

The white working class is the constituency most likely to vote for Trump. An NBC/Wall Street Journal survey has him leading Hillary Clinton among non-college-educated whites 49-36 percent, a larger lead than among any other demographic.

But given how these voters perceive debt, that support may be more fragile than we think. As a businessman, Trump is known for not paying his debts to small vendors, who for the most part cannot afford to challenge his actions in court. He has repeatedly and intentionally failed to pay dishwashers, waiters, plumbers and even his own lawyers.

Over the last three decades, Trump was involved in more than 3,000 lawsuits, including cases where he drove small family firms out of business. Trump says he does not pay when the work does not meet his standards. If that is true, it means Trump is disastrously bad at choosing people who will do good work, which makes one wonder how he would go about hiring staff once in political office.

But everything indicates that Trump is lying on this point, and that refusing to pay his debts is simply a business strategy.

To many readers, not paying debts will seem like just one in the long string of Trump’s transgressions — what’s a few unpaid bills compared to saying he would ban Muslims from entering the country, or jokingly inviting Russia to meddle in American elections, or criticizing the family of a fallen soldier?

But white working-class voters in the Midwest may not see it that way. To them, paying what you owe is one of the central aspects of their identity as moral human beings. Ads in Midwestern swing states featuring the real people whom Trump has stiffed — working class people, exactly the ones whom these voters can identify with — could well prove effective.

Clinton’s overall lead is so large at this point that she may be tempted to take it for granted. But attempts to turn Trump’s core supporters against him could influence down-ballot races as well.

Trump will claim that he behaves no differently from other successful businessmen (the answer to those who say Trump is successful: Sure, until his next bankruptcy). But refusing to pay your debts is not standard practice in construction or any other industry in America. The stories of the people who lost their small businesses because of Trump would resonate emotionally, because they are a window into the nominee’s values, and to how he would run the country: He would accumulate debt and threaten not to repay America’s creditors. In a word, he would turn the United States into a “liberal” country, as our interviewees understand that term.

My colleague Steve Hoffman asked one of our respondents what single lesson she learned from her parents that influences how she sees the world now.

Her immediate response was the three words that should be the cornerstone for any anti-Trump efforts in the Midwest: “Pay your bills.”

Monica Prasad is professor of sociology and faculty fellow in the Institute for Policy Research at Northwestern University.