It appears the hatchet is officially buried.

After a bitter and prolonged primary battle involving Rick Santorum and Mitt Romney, Santorum on Saturday attended his first high-profile campaign event on Romney's behalf. Santorum helped open a Romney campaign office in Greensburg, Pennsylvania, that's shared with the state Republican Party.

Not only did Santorum offer high praise for Romney, but he played political offense and defense for his former rival.

Claiming the "republic is at stake" in the presidential election because of President Barack Obama's failed policies, Santorum said, "One man is who we have to put our trust in to go out and fight that battle, and win that battle. And we must rally behind and do everything we possibly can to support Governor Mitt Romney so he's the next president of the United States."

Santorum, a former senator from Pennsylvania, added: "Pennsylvania is where it's at... If Pennsylvania goes Republican, Mitt Romney will be the next president of the United States."

As Democrats question Romney's tenure at his former private equity firm Bain Capital and call for him to release more tax returns, Santorum defended Romney.

Santorum called Romney a "solid businessman who understands how to make things work" with "great private sector experience."

When asked about the tax return issue, Santorum said, "I think all of this is a distraction. It's pretty clear, from the past, this issue has been vetted over and over. You know, during the primary."

Romney has released his 2010 taxes and has said he will release those for 2011. But during an interview with CNN, Romney said he would not release more.

Santorum's praise is a far cry from the fight between the two men during the GOP primary.

Until Santorum ended his bid for the Republican nomination in April, his campaign sustained a harsh back-and-forth with Romney's team. At various points, Santorum questioned Romney's ability to win the White House and claimed Romney would be "the worst" candidate to pit against the president on the issue of health care.

Though the pitched primary language was virtually absent at the Saturday event, there was one moment that Santorum seemed to dig at Romney.

When asked about his comment that Romney would be the worst candidate on the health care issue, Santorum said: "I said on the issue he would have trouble. And I think he's, you know, had a little trouble coming out of the gate on this issue.

"But the bottom line is, he's far better than Barack Obama on this issue."