HARRISBURG -- State House Democrats pulled off a major political coup in November 2006 when they regained control of the chamber by the slimmest of margins -- one vote.

This year, Democrats are working feverishly to hang onto that power and possibly increase their 102-101 margin. But things haven't been easy, what with "Bonusgate," Attorney General Tom Corbett's ongoing investigation into illegal state-funded political bonuses, and with many voters focusing on the intense presidential battle between Barack Obama and John McCain.

Democrats also are facing a strong counterattack by House Republicans, who want to take back control of the House, which they ran from 1995 to 2006. The GOP thinks it can take over some districts now represented by Democrats, but Democrats also are optimistic about success in areas where Republican incumbents are retiring, especially in southeastern Pennsylvania.

While Democrats control the House and have held the governor's office since Ed Rendell took over in January 2003, their chances of capturing the state Senate are virtually nonexistent. Republicans hold a 29-21 advantage now, and few seats are expected to change hands Nov. 4. Republicans have run the Senate for almost all of the past 25 years.

"Obviously, Bonusgate has cast a shadow over the Democrats' hopes for expanding their lead in the House, but they do see opportunity in some places, such as Bucks County and other parts of southeastern Pennsylvania," said Christopher Borick, a political science professor and pollster at Muhlenberg College in Allentown. "The southeast is, potentially, the hot corner of the state for Democrats."

He and G. Terry Madonna, a political science professor and pollster from Franklin & Marshall College in Lancaster, said House Democrats should benefit from recent voter registration gains. There are now more than 1 million more registered Democrats than Republicans in Pennsylvania.

And at least until recently, Mr. Madonna said, "Democrats have benefited from the 'enthusiasm gap,' " meaning voters' interest in Mr. Obama could boost the overall turnout and help Democratic House candidates.

But now, with the excitement generated by Republican vice presidential candidate Sarah Palin, "that gap has narrowed," Mr. Madonna said. "Republicans are more enthusiastic with Palin on the ticket."

How much the Bonusgate probe will affect state House races remains a question. To date, all 12 of Mr. Corbett's arrests have been of House Democratic lawmakers or staff members, including the former No. 2 Democrat, ex-Rep. Mike Veon, and Rep. Sean Ramaley, both of Beaver County.

Until Mr. Veon lost his seat in 2006, he had been a close ally of House Democratic leader Bill DeWeese, of Waynesburg, who is facing a tough race this fall.

Mr. Corbett has said additional arrests are likely in his investigation, and some state officials expect them to hit before Sept. 30.

One House district where Republicans have hopes includes Greene County and part of Fayette, the district that Mr. DeWeese has represented for more than 30 years.

His Republican opponent, Greg Hopkins, a former professional football player from Nineveh, Greene County, did well in 2006 before losing 53-47 percent, and is back again this year.

"I am out knocking on doors every day, and I think DeWeese is in trouble," said Mr. Hopkins, 36, who played for arena football teams in New York, Indianapolis and Los Angeles.

Mr. Corbett alleges that some House Democratic staffers, in 2006, spent days and even weeks working on political campaigns and later were illegally rewarded with at least $1.2 million in state-funded bonuses. Mr. DeWeese contends that if anything improper occurred, he knew nothing about it and has done nothing wrong.

But Mr. Hopkins said, "Constituents I've talked to aren't buying that. Two years ago, they were upset with DeWeese over the [2005] pay raise, but a lot of them said, 'Well, he's always been my guy, he knows my cousin, things like that,' and they gave him a second chance. But to have more than $1 million slip out during your watch, you're either not telling the truth or you're an incompetent leader."

Either way, Mr. Hopkins contended, the longtime Democratic incumbent needs to be replaced.

Mr. DeWeese sees things quite differently. He said he too has spent months shaking hands around his district and is "wearing down my Marine Corps boots." He remains optimistic about re-election.

"My door-to-door campaign has galvanized renewed enthusiasm for my political and legislative work," he said last week. "I have had my game face on since the start of this campaign. On Election Day, the Bill DeWeese campaign team will be eminently competitive, in spite of the excitement of the past two years."

That last remark was apparently a reference to the Bonusgate probe, but Mr. DeWeese wouldn't elaborate.

Another Western Pennsylvania seat where Republicans are hopeful is now represented by Rep. Frank Dermody, D-Oakmont. He is being challenged by Fawn Supervisor Jason Davidek, 29, for the seat based in the Allegheny Valley.

Mr. Dermody recently was one of about 15 incumbent Democrats to call for Mr. DeWeese to step down as leader. Some political observers saw that as an attempt to distance himself from Mr. DeWeese and Bonusgate.

Mr. Davidek said Mr. Dermody called on the House leader to step down only after "I issued a press release saying he should make his position about DeWeese known to constituents."

The challenger said that Mr. Dermody is part of the entrenched House Democratic leadership that should be replaced. He said many Western Pennsylvanians, "are fed up with wasteful state spending and corruption in Harrisburg."

But Mr. Dermody said, "I'm working very hard" to get a 10th term in the House.

"I am talking to people about the issues that are important to the district. I'm knocking on doors and having town meetings. Democrats are right on the issues, like energy and health care. We'll keep our majority and gain seats in the House."

Freshman Rep. Matt Smith, D-Mt. Lebanon, also said that Democrats' chances on Nov. 4 should be enhanced by recent voter registration increases. But Mr. Smith, who is also calling on Mr. DeWeese to step down as House leader, said Democrats, in order to prosper, must "focus on legislative reform issues," such as cutting by 20 percent the Legislature's $332 million budget, limiting the size of campaign donations and creating a nonpartisan redistricting process.

"People want the Legislature to operate in a more efficient manner," Mr. Smith said.

This year, almost all incumbents and challengers "are talking like reformers," said Mr. Madonna. "What are they going to say -- that they LIKE the way things are going in Harrisburg?"

The Bonusgate scandal hasn't been much of a factor in Philadelphia and its four suburban counties, where Democrats are shooting to pick up one or more Republican-held seats.

Mr. DeWeese said that Democrat Rich Costello, a former Fraternal Order of Police official who's challenging longtime Republican Rep. John Perzel in part of northeast Philadelphia, "is well positioned to give John the fight of his life."

But Republicans doubt that Mr. Perzel is in trouble, saying GOP presidential candidate Mr. McCain will do well in Mr. Perzel's area and help the former House speaker in re-election.

Philadelphia political analyst Jeff Jubelirer said that Democrats have better hopes of capturing another northeast Philadelphia district, the one held by veteran Republican Rep. George Kenney, who's retiring this year.

Democrats also hope to win the suburban Delaware County seat held by GOP Rep. Ron Raymond, another incumbent who's retiring this year.

There are other Republican-held seats in suburban Bucks, Chester and Montgomery counties where Democrats might pull upsets.