Mitt Romney visited the shuttered headquarters of the bankrupt Solyndra solar energy company Thursday, venturing into the physical heart of his political argument against President Obama’s stewardship of the economy.

The Republican presidential candidate has repeatedly invoked the failed energy company as evidence of Obama’s economic failure and his hostility to the private sector.

“Two years ago, President Obama was here to tout this building and this business as a symbol of his stimulus” Romney said, standing in front of the gleaming building, which now has a red “For Sale” sign hanging from the roof. “Well, you can see that it’s a symbol of something very different today, it’s a symbol not of success, but of failure.”

Romney and his allies are hoping that Solyndra will become a household name, a catch-all example of what Republicans have argued is Obama’s assault on free enterprise and preference for big government.

“I’m afraid the reason that the stimulus has been unsuccessful, that the turnaround has taken so long to occur, that the recovery has been so tepid is that the president fails to understand the basic nature of free enterprise in America,” Romney said. “He thinks that government-dominated decisions like this make America stronger. They make us weaker. They send the wrong message.”

With loans backed by $535 million of taxpayer money, Solyndra was a big beneficiary of the Obama administration’s focus on trying to build a green-jobs economic sector. But in the fall of 2011, the company filed for bankruptcy and fired about 1,000 workers. The Solyndra failure has become one of Romney’s main counter-arguments to attacks from the Obama campaign about his tenure as a private-equity executive at Bain Capital.

“If you look at this building behind us, this is not the kind of building that is filled by private enterprise. This is the kind of enterprise, the kind of building that’s built with a half a billion dollars of taxpayer money,” said Romney. “It’s not just the Taj Mahal of corporate headquarters. You probably also heard that inside there are showers that have LCD displays that tell what the temperatures are of the shower water. And the robots inside actually provide Disney music tunes.

The Romney campaign shrouded the visit to Solyndra in secrecy, suggesting to reporters that Obama and his aides might have tried to thwart the appearance.

“I think there are people who don’t want to see this event occur, don’t want to have questions asked about this particular investment, don’t want to have people delve into the idea that the president took a half a billion dollars of taxpayer money and devoted it to an enterprise that was owned in large measure by his campaign contributors,” Romney said. “This is a serious conflict of interest. This ought to be a big story, and I think there are a number of people among the president’s team who don’t want that story to get out. We wanted to make sure it did.”

Romney’s full-throated attack on Solyndra and his indirect defense of Bain come as Obama and his allies turn their attention to Romney’s record as governor. The campaign released a five-page memo and a four-minute Web video Wednesday characterizing Romney’s leadership of Massachusetts as a failure. The Web video uses dire music and a series of interviews with local elected leaders to describe fees Romney raised and the increase in state debt during his tenure.

At a news conference in Massachusetts, top Obama adviser David Axelrod, who was shouted down by Romney supporters, said Romney’s record in the private sector left Massachusetts near the bottom in job creation.

“Mitt Romney created more jobs in the state of Massachusetts than President Obama has for the entire nation,” Romney spokeswoman Andrea Saul said. “President Obama has failed to meet his own goal of 6 percent unemployment and has a net negative record on job creation.”

Democratic campaign advisers said criticizing Romney’s gubernatorial record bolsters Obama’s claim that the Republican’s Bain years don’t qualify him to lead in the public sector. “It wasn’t happenstance that Massachusetts struggled under Romney,” Axelrod said. “He brought the orientation of a financial engineer.”

Under Romney, Massachusetts was ranked 47th in job creation, yet Romney pointed to the unemployment rate, which dropped during his tenure.

“When I was governor of Massachusetts, we took the unemployment rate from 5.6 percent down to 4.7 percent. I think 4.7 percent’s a pretty good number. My guess is the people of America would be very pleased if they could see a number like 4.7 percent . I’d hope to be able to get there if I were president,” Romney said. “But I can tell you that my experience in the economy tells me how it is businesses make decisions to hire. . . . I want to use that knowledge to get Americans working again.”

Staff writer Amy Gardner contributed to this report from Washington.