Democratic candidates claimed big victories in three Philadelphia-area "collar counties" on Tuesday in one of the starkest warnings for Republicans across the nation that their prospects among suburban voters are at risk.

For the first time since the Civil War, Democrats will hold all five seats on the Delaware County Council, south of Philadelphia.

In Chester County, Democrats won a majority of council seats for the first time since the modern parties aligned. Democrats also won races for county sheriff and district attorney.

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And in Bucks County, Democrats claimed two of three seats on the County Council to win a majority for the first time since 1983.

Clinton also won Chester County in 2016, becoming just the second Democrat to win it in the last 13 presidential contests.

But the local results this year, Democrats say, suggest more long-lasting fallout for the GOP.

“There’s a repudiation of the Republican Party brand that is not going anywhere. That is a trend that is going to continue as long as and probably well after Donald Trump is the standard-bearer for the party,” said Mark Nevins, a longtime Philadelphia-based Democratic strategist. “This is a commentary on the Trump effect on Republicans across the country.”

Republicans, too, acknowledged the challenge they face in the year ahead as Trump prepares to defend an electoral coalition that runs through exurban and suburban areas.

“Those results are a reflection of what should be a growing concern for the GOP: voters. It's not enough to turn out your base, at some point you have to grow it, especially given the changing demographics and politics of suburban communities,” said Michael Steele, a former chairman of the Republican National Committee and a Trump skeptic.

“When you have to hold an increasingly larger share of suburban voters because you have no juice in the cities they surround, it becomes more difficult to win races when Democrats are able to increase their share of that vote,” Steele said, pointing to another state that voted on Tuesday: “Can you say Virginia?”

But the local results are far from determinative in a state where Trump ran up the score far from the urban cores. Nevins said he continued to worry about Democratic performance in other parts of the state.

“In 2016, Pennsylvania was lost or won, depending on how you look at it, in the northeast. The question is whether or not white non-college voters in northeast Pennsylvania are following the trend that suburban voters are in southeastern Pennsylvania or even in the doughnut around Pittsburgh,” Nevins said. “And I don’t know the answer to that yet.”