It was a local race in an off-year election that ordinarily wouldn't have created a ripple of interest outside the confines of Montgomery County.

But when Josh Shapiro and Leslie Richards made history by securing a Democratic majority on the county's Board of Commissioners for the first time, it was an event of national significance, in the view of Michael Hagen, a political science professor at Temple University.

It spoke to a stunning turnabout in the county's political landscape, and a blue tide that continues to rise in Philadelphia's once-solidly Republican neighboring counties. Pennsylvania again will be a battleground state in the 2012 presidential election, he said, and those counties could decide the outcome.

Republicans in Bucks, Chester, and Delaware Counties fared better Tuesday, maintaining party control, but the GOP has reason to be concerned about the Montgomery County results, Hagen said.

"If you look at the trends in voter registration, it's hard to say it isn't moving in a Democratic direction," Hagen said.

For their parts, Shapiro and Richards downplayed any national significance. "We'll let the pundits decide," Shapiro said.

Both he and Richards said they were focused on day-to-day issues. "We know we have to get our county fiscal house in order," Shapiro said. "We're going to have a very aggressive transition team so we can hit the ground running."

Richards said she hoped the new board, which will include outspoken GOP incumbent Bruce L. Castor Jr., would be more collegial than its predecessor.

By law, the minority party gets one seat on the board, and Castor narrowly outpolled his running mate, Lower Merion Commissioner Jenny Brown.

"I"m not happy with the results," said Castor. But he said he was ready to work with the victors, "to help them implement the agenda ... so long as it doesn't conflict with my conscience."

Montgomery County Republicans did win the sheriff's office, and District Attorney Risa Vetri Ferman was unopposed.

The GOP dominated countywide races in Delaware County, but took some local hits. Chester City elected a Democratic mayor for only the second time in the last century, choosing Councilman John Linder over two-term incumbent Wendell N. Butler. Democrats also captured the controller's office and two council seats.

Democrats also made gains in the boroughs of Folcroft, Media, Morton, Norwood, and Sharon Hill, and in Upper Darby Township, but lost ground in Haverford Township and Ridley Park and Brookhaven Boroughs.

David Landau, chairman of the Delaware County Democrats, said he was encouraged by the results. "This victory was about building infrastructure and campaign organization," Landau said.

The GOP monopoly in Chester County continued as the party won all the top-tier races. Incumbents Terrence Farrell and Ryan Costello were on their way to new terms on the Board of Commissioners.

Democrat Kathi Cozzone, also an incumbent, was reelected.

In Bucks County, Republicans repelled an energetic challenge from the Democrats and extended their 24-year hold on the Board of Commissioners.

The Montgomery County campaign was especially expensive, with the two parties spending a combined $1.7 million. It also was acrimonious. Shapiro and Richards made an issue of Castor's contrarianism, and said it resonated with the voters. "People are frustrated," Richards said.

They portrayed Brown as a member of the tea party, although Brown said she did nothing more than meet with tea party members. "All these things they said about me and put in their literature don't have a basis in reality," she said.

About 32 percent of the 532,784 Montgomery County registered voters turned out for the election.

One reason Castor cited for the GOP defeat was the Democrats' registration advantage, 36,000. Hagen noted that in 2000, the Republicans had a 100,000 advantage.

Of the overall registration trends in the counties, he said, "It's hard to see that reversing."