By Gerald F. Seib 

When Michigan's Macomb County, just north of Detroit, flipped to vote Republican in the 1980s, it became the very symbol of the "Reagan Democrats" -- previously loyal middle-class Democratic voters who abandoned the party in that decade. In 2016, Macomb County did it again: It voted for Republican Donald Trump by 12 percentage points over Democrat Hillary Clinton.

This year? Macomb County flipped back. A majority of its voters went for Democrats in statewide races for governor and a U.S. Senate seat.

As that suggests, the most intriguing and important results of this year's midterm elections came in the upper Midwest -- the traditional industrial heartland that provided President Trump the biggest dose of rocket fuel he needed for his shocking presidential election victory two years ago.

This year, the very states that propelled Mr. Trump across the finish line -- Michigan, Wisconsin and Pennsylvania -- all went the other way. All elected Democrats to both the U.S. Senate and to their governor's offices. In all three, Democrats won a majority of the House votes.

That outcome has broad political significance on two fronts. First, it raises questions about the power of Trump trade policies, which seem almost designed to appeal specifically to workers in those three industrial states. And second, the outcome in the upper Midwest tells us a lot about the intriguing early contours of the 2020 presidential campaign map.

It's always possible to read too much into one set of election results, of course. Democrats this year had the natural advantage that always accrues to the party out of power in a president's first midterm election. In both Pennsylvania and Michigan, their chances statewide were enhanced by the fact that Republicans ran what were widely considered to be weak candidates for governor.

Moreover, as Mr. Trump took great pains to remind viewers on a Fox News Sunday interview this week, he wasn't running personally: "My name wasn't on the ballot." So it's risky to assume how he would have done, as opposed to how other Republicans did.

Still, Mr. Trump tried hard to make the 2018 elections about him, telling voters repeatedly to act as if he were on the ballot. More striking, though, is the extent to which Trump trade policies -- decrying existing free-trade agreements, renegotiating the North American Free Trade Agreement, imposing steel tariffs on trading partners and launching a virtual trade war with China -- didn't translate into electoral success in the states that seemed most likely to be grateful for steps designed to protect traditional industrial areas of the country.

That doesn't necessarily mean voters there don't appreciate Trump trade efforts. It may simply mean other issues were more on the minds of voters. Democrats everywhere found that health care was at least as high a priority as economic issues.

Rahm Emanuel, the Democratic mayor of Chicago, says Democrats won in the upper Midwest because they stressed not "sizzle but substance" -- school funding, infrastructure -- while Mr. Trump stressed cultural issues, particularly immigration. "Trump ran on culture and walked away from the economics," Mr. Emanuel says.

Moreover, a study of Trump voters and political independents in Macomb County last year by Democracy Corps, a research organization run by Democratic pollster Stan Greenberg, found that support for the president was offset by deep misgivings about his style.

Whatever the cause of Republican setbacks in the Rust Belt, the results there and around the country suggest an intriguing electoral map is taking shape for the 2020 presidential race, presenting challenges for both parties.

For Democrats, a key will be to find a candidate capable of holding onto those voters in the upper Midwest -- moderates who again will assume their role as the ultimate swing voters. In that region, they need to hold on to Minnesota, the rare state where Republicans turned a couple of House seats their way. Meanwhile, some states seem to have moved more clearly toward the Democratic column -- Nevada and Virginia -- while the key state of Ohio seems to have moved away.

For Mr. Trump, the midterm results suggest he will have to fight what Doug Sosnik, who was political director for President Clinton, calls a "two-front war."

He will need to regain his grip on those upper Midwest states, obviously. But this year's results suggest he now also has to worry about GOP slippage in states in the South and Southwest that Republicans once took for granted.

Democrats came close to winning a governor's race in Georgia and a Senate race in Texas. Moreover, Democrats prevailed, barely, in a key Senate race in Arizona.

And then there is Florida, home of two photo finishes in big Senate and governor's races this year, both carried by Republicans with the narrowest of margins. Nobody should be surprised if 2020 is decided, once again, in the Sunshine State.

Write to Gerald F. Seib at jerry.seib@wsj.com

(END) Dow Jones Newswires

November 19, 2018 12:03 ET (17:03 GMT)

Copyright (c) 2018 Dow Jones & Company, Inc.