"This is the rare political event here or in the country where you have an upset landslide," said Democratic party activist and former Congressional candidate Dan Wofford. "It's a true watershed election that breaks the Republican stranglehold in Chester County."
The last Democrat to represent Chester County in any Harrisburg legislative seat was state Rep. Sam Morris, who lost his seat to Gerlach in 1990.
The last Democrat to represent Chester County in the state Senate was Septimus N. Niven, a farmer from London Britain Township, who defeated Republican D. Smith Talbot by 300 votes, said political historian Craig Tucker.
Republicans in this century were dumbfounded by not only their loss but the magnitude of it.
"Not even Rendell's numbers were that good," said Republican county controller Valentino F. FiGiorgio 3d. "It is hard to analyze because it is unprecedented. We need to figure out what message our base was sending."
But Democrats had no problem figuring it out, saying the race's outcome spoke to the anger voters are feeling at Washington, Harrisburg and everywhere in between.
"There is a frustration that crosses party lines," said Wofford. "People want change, they want government to start solving problems and they want an end to partisanship."
Many credited Dinniman's win to the fact that he has been a county commissioner for 15 years. People knew him, they felt comfortable with him and they liked him.
But all said that Dinniman ran a textbook campaign, one that unified the normally fractious Democratic party in Chester County, and one that attracted significant help from outside the district. He also had the backing of organized labor and environmentalists, all of whom were working to get out the vote.
"The Democrats worked much harder and more effectively than the Republicans in this race," said Republican Jack Marshall of Tredyffrin Township. "It was blood and guts - they were working like old-time committee men."
Dinniman won not only the Democratic vote, but a significant number of Republicans crossed party lines to cast their ballot for him, observers said.
Of the district's 173,803 registered voters, Dinniman received 21,478 votes to Aichele's 16,733 votes according to unofficial returns from Chester and Montgomery Counties. Turnout was around 22 percent.
DiGiorgio said that in Aichele the party felt that it had a "slam dunk candidate" for the district - a moderate woman with government experience. "The slam dunk lost by 13 points," he said.
Analyst and pollster G. Terry Madonna said that on a day of seismic upsets in the political landscape of Pennsylvania, the significance of Dinniman's win should not be underestimated.
"This is a major inroad by a Democrat in a solidly Republican district," he said. "That should cause Republicans at the state level to be concerned about the ability of the Democrats to extend their reach in the suburbs."
Democratic political strategist Mark Nevins said the win could be traced back to Rendell's first gubernatorial bid in 2002 when he organized a massive voter registration drive in Southeast Pennsylvania.
The Kerry presidential campaign built on that in 2004, and in 2005 Democrats had their first taste of victory when they elected two Democrats to the Tredyffrin Township board of supervisors.
"Democrats now have the manpower and the know-how to turn out a huge vote in Chester County," he said. That could be a problem for Gerlach as he faces Democrat Murphy for a second time for the Sixth Congressional district seat.
"This is not good news for Gerlach," said Madonna. "He will have a state official in his backyard who can help plan his political demise."
Contact staff writer Nancy Petersen at 610-701-7602 or email@example.com.