America’s suburbs: They’re sprawling, replete with shopping centers and bike paths – and they’re often where presidential elections are won or lost.

But in a potential problem for the presumptive Republican nominee, Donald Trump has not fared so well in the ‘burbs so far this cycle.

Even as the billionaire businessman attracted more primary votes this year than any Republican candidate in history, the battleground occupied by America’s middle class is where he may have to make inroads if he is to defeat Hillary Clinton in November.

"Donald Trump speaks in language that many Americans like -- but they're not suburbanites,” said Larry Sabato, director of the University of Virginia Center for Politics.

Take Washington state’s Duvall, a small but fast-growing suburb of Seattle. It's long been friendly territory for Republican candidates. But in last month's state primary, the Republican share of the vote in Duvall was 11 percent lower than it was in the 2008 primary. A GOP vote decline was‎ seen in every city in the wealthy suburbs east of Seattle.

But it wasn't just Washington state.

In North Carolina, Trump lost three of the four largest counties, including those areas around Raleigh and Greensboro, where he won just 32 percent and 29 percent, respectively.

In Iowa, he lost Polk County – which includes Des Moines -- to Florida Sen. Marco Rubio, as well as the counties around Davenport and Iowa City.

In the D.C. suburbs of Virginia, a state that is swing territory in the general election, Trump lost Prince William County with 33 percent and Loudon County with 28 percent.

He also lost in the suburbs in the critical state of‎ Ohio. He lost Cuyahoga with 32 percent, Franklin County with 22 percent and Hamilton County with 32 percent. Those counties include suburbs around Cleveland, Columbus and Cincinnati, respectively. Trump, though, started off at a unique disadvantage in the Ohio primary, as he was competing against Ohio Gov. John Kasich, who won the state.

By contrast, in the Democratic primaries, Hillary Clinton won all those counties except for a couple she lost to Bernie Sanders in Iowa.

Joel Connelly, who is covering his eighth presidential election for the Seattle Post-Intelligencer, suggested some suburban voters just aren’t sold on Trump’s message.

"Suburban voters want competence," Connelly said. “They are looking for someone who will govern efficiently, not get us into wars, not create chaos, because they live in an orderly world."

Where Trump did remarkably well is among rural voters and working-class white voters in urban areas. His message that the economy is broken due to bad trade deals made by career politicians resonates – it’s a message Trump hammered repeatedly on the campaign trail this week, even threatening to pull the U.S. out of NAFTA if necessary.

"If your ports aren't active, then your rural agriculture areas will suffer," said Don Benton, Trump's Washington state campaign director. "Your inner city, if you don't have jobs, there's more people unemployed. So certainly it could have something to do with the fact that suburbia has always been a little insulated from the rest of the country."

Republican Party leaders insist the suburbs will be in play come November, even though soccer moms and college-educated voters are proving a tougher sell for Trump.

Clinton is not without her challenges, either. She continues to fight high negatives even among white women, a group she has been targeting throughout the campaign for support.