MILWAUKEE, Wisc. — Barack Obama wasn’t entirely accurate on what we’re clinging to here in the embittered heartland.

Guns, God, and xenophobia? Nah. Around the Great Lakes, it’s our water and a bad attitude.

Now that Atlanta’s suffering a drought and Las Vegas is paying people to rip up lawns, Great Lakes states are seized both by a fear that the Sunbelt will take that water away and a gleeful hope that our supply will be what at last brings Sunbelters, thirstily chastened, back to live here.

More than a quaint regional folly, this matters to the rest of America for three reasons. First, that many Midwesterners believe it means they still don’t acknowledge why the giant shift of people to the Sunbelt really took place. Second, it means a swath of cities from Buffalo to Duluth will remain Layoff Land, a drag on the nation’s economy. And finally, it’s here that you’ll find next fall’s likely swing states. Us daydream believers will choose your next president.

Senator Obama did get one cling right: anti-trade sentiment. Many people in the Rust Belt really are ticked at how they imagine liberalized trade to have worked out.

So Mr. Obama pandered to them. He blasted the North American Free Trade Agreement. He denigrated China. So did Hillary Clinton. To the extent the Democratic race has gone protectionist, it is because protectionism appeals to voters around the Great Lakes.

But most manufacturing job loss is because it takes fewer people to make things. Exports, meanwhile, fuel the region’s successes. Companies and industries that embrace trade do well. Restricting it would be disastrous.

Still, people believe in miraculous autarky. If only we cut off China, we’d return to days when the pay was high, unions were boss, and jobs were for life. Stagnation, in this view, had nothing to do with us. It sneaked in from elsewhere.

Such magical thinking is paralleled in our latest salvation: the Sunbelt’s thirst. Before China, our factories were heading to the South, and so were all the moving vans. Metro Atlanta gained more people since 2000 than all of those who live in metro Rochester, N.Y. They grow, we stagnate.

Now, people say, Atlanta’s finally out of water, so the prodigals will have to return if they want any. The man on the street says this. Serious, thoughtful people say it. “This is a very big economic development tool for the Great Lakes region,” said Todd Ambs to business leaders in Milwaukee in March. Mr. Ambs runs the water division for Wisconsin’s Department of Natural Resources and knows more about water than I ever will. The message, he says, is that if southerners are thirsty, “you can come back to the Great Lakes.”

Won’t happen, says John Kasarda, who knows more about economics than I ever will. Mr. Kasarda, who researches entrepreneurship and demographics at the University of North Carolina, says there’s simply no evidence that constrictions in water supply alone will make people abandon a burgeoning region. A far bigger determinant, he says, is an area’s “pro-enterprise atmosphere.”

Even the critics who see Atlanta’s growth as sprawl don’t see drought as ending it. “You can’t stop the growth in metro Atlanta,” said environmentalist Joe Cook, who runs a clean water group one valley over from Atlanta and who points out that Atlanta was built in a dumb place, water-supply wise. Still, he says, “You can choose to live pretty much wherever you want to, as long as you have some employment. … So if there aren’t any jobs in Milwaukee or Detroit or wherever, then people aren’t going to live there.”

Why are so many of the jobs in the South, far from the Great Lakes? An encouraging attitude toward growth, says Mr. Kasarda, a “flexible, non-union environment,” and lower taxes. “They put out the red carpet for business,” he says. It worked. Businesses came and people followed.

The Great Lakes states’ regulators tend to be more hostile, their taxes more confiscatory. There are stabs at improvement. But last year, Illinois’ governor proposed a new $6 billion tax on business and the Wisconsin Senate floated a new $15 billion payroll tax. More moving vans fueled up.

No, they’re not moving back. Atlanta will find other water, or employers will find another city on another Southern river. Consider their choice: Move north and subject yourself to capricious regulators, high taxes, and petulant unions — or stay and install low-flow plumbing and let the lawn go brown. Tough call, eh?

Meanwhile, places that won’t admit their regulators are capricious are choosing your president. Mr. Obama will likely get the nomination after he held Mrs. Clinton to a victory of 15,000 votes in Indiana. A major part of that was the way Lake County — Gary and environs — went heavily for Mr. Obama. Gary, as ruined as a city can get without the use of tactical nukes, has plenty of Lake Michigan water. It just lacks prosperity and much of a clue about regaining it.

When Mr. Obama campaigned there in early April, he said that what was good for Gary was to raise federal taxes and to stop “companies shipping jobs overseas.” This apparently was well received. People believe the damndest things when they make a habit of ignoring reality.

Mr. McIlheran is a columnist for the Milwaukee Journal Sentinel.