None of Corbett's major initiatives -- new taxes to bolster transportation projects, prospective rollbacks in public pension benefits and the privatization of state-controlled liquor and wine sales _ got majority support despite Republican control in both houses.
Turnover among Corbett's top advisers has been steady since he took office in 2011. His longtime spokesman recently stepped down as part of an overhaul of his communications shop, and his nominee for education secretary was dismissed.
Most of the Democrats running in the May 20 primary -- or thinking about it -- have high-level experience in state government.
Contenders include U.S. Rep. Allyson Schwartz, former state revenue secretary Tom Wolf and two former environmental protection secretaries who served in Gov. Ed Rendell's administration, Katie McGinty and John Hanger.
Two of the undeclared hopefuls have won statewide campaigns: state Treasurer Rob McCord, who has formed a campaign committee that lets him raise money, and former state Auditor General Jack Wagner, a Pittsburgh resident who lost this year in that city's mayoral primary.
Other declared candidates are Pentecostal minister Max Myers and Lebanon County Commissioner Jo Ellen Litz. State Sen. Mike Stack, of Philadelphia, has said he is considering running.
"This is an incredibly strong field," said Terry Madonna, the Franklin & Marshall pollster who oversaw the recent survey.
The Democratic State Committee meets Feb. 8 to endorse its primary favorite, something that requires a two-thirds majority vote - a tall order even for a popular candidate.
On websites and in public appearances, the candidates are working to define themselves apart from the pack.
Schwartz touts her strong recognition in the heavily Democratic Philadelphia media market.
Wolf, who briefly ran for governor in 2010 but dropped out, raised eyebrows when he announced he would plow at least $10 million of his own money into his primary campaign.
Hanger, who served as a state utility regulator for five years before Rendell appointed him to head the DEP, is emphasizing wide-ranging policy proposals that include tougher gas-drilling laws, the revocation of state funding for failing charter schools and the decriminalization of marijuana.
McGinty's campaign stresses her governmental and private-sector experience in environmental protection and her Philadelphia upbringing as the ninth of 10 children.
Campaign aides played down the threat of a divisive primary fight that could weaken the eventual nominee, arguing party activists are united to oust Corbett.
But Christopher Borick, a pollster and political scientist at Muhlenberg College, said the absence of a clear front-runner in a crowded race could result in "a very muddled war of attrition'' among Democrats.
"If (Corbett) is going to have trouble rallying the troops based on his performance, he may have better luck by pointing out the threats from whatever Democrat is nominated," he said.