PITTSBURGH He has seen the polls and heard the whispers in his party about his reelection chances.

But Gov. Corbett on Wednesday put to rest any lingering doubts: He is running for another four-year term.

"We are not finished," he told a crowded room of supporters gathered at the Sen. John Heinz History Center, where he formally kicked off his "Promises Kept" reelection campaign.

Throughout his announcement, Corbett gave tacit signals that he was aware his campaign for another four years in the state's top job faces obstacles, including an ever-growing field of Democrats jockeying to challenge him in next year's election. But the governor kept circling back to his theme, that he went to Harrisburg and kept the promises he made when he ran for governor four years ago.

"Were the decisions I made to get here tough? Yes. Were they politically expedient? Never," he said. "But leadership and governing is about doing what's right, not what's easy."

During his 35-minute speech, Corbett focused on what he considered his administration's successes rather than laying out specific goals for a second term.

He said his administration had reined in spending, balanced budgets, created jobs, and had not raised taxes. Economic accomplishments, he said, included an improved business climate in Pennsylvania and growing the state's energy sector - in particular, gas drilling in the vast Marcellus Shale formation.

Corbett also touched on what will perhaps be the issue on which he is most vulnerable as he hits the campaign trail: public education funding. The administration made deep funding cuts in the governor's first year in office, a point on which his opposition has hammered him.

But Wednesday, Corbett countered that view, saying that when he came into office, federal stimulus money earmarked for education had masked the state's declining ability to dramatically increase funding for public schools every year.

When that money ran out in 2011, Corbett's first year in office, schools took a hit. But there was no other money he could turn to, Corbett said, and his administration used what little money was available to increase state support for basic education.

"We have a responsibility to provide a good education to all children in Pennsylvania, but it starts with an honest discussion about education funding," he said.

After announcing his campaign in Pittsburgh - he did so at the same place he did four years ago - Corbett flew across the state for a stump speech in Pittston, Luzerne County. Stops in Philadelphia and Montgomery County are scheduled for Thursday.

In Pittston, Corbett visited the Linde Corp., which specializes in Marcellus Shale, municipal, and utility pipeline construction. He briefly toured the plant before speaking to about 50 workers, local politicians, and other spectators.

After touting job growth that Linde has experienced due to Marcellus Shale operations, Corbett said natural gas drilling would provide jobs for generations to come.

"Energy equals jobs," he said. "You couldn't pick a better place to demonstrate that than right here."

Corbett's campaign is dubbing this week's swing the "Corbett-Cawley Promises Kept Re-Election Tour."

Polls and pundits have identified Corbett as one of the most vulnerable incumbent governors. Last week, only 20 percent of respondents in a Franklin and Marshall College poll of 628 registered voters said he deserved reelection. The poll found 44 percent of Republican respondents said he should not seek reelection.

At least eight Democrats are seeking the party's nomination to challenge Corbett, and many of them on Wednesday reiterated they thought the Republican's policies had been hurtful to Pennsylvanians.