Bill Clinton is typically described as the empathetic, feel-your-pain guy. But his greatest political skill may be as a formulator of arguments — the explainer in chief.

At the Democratic National Convention on Wednesday night, he did not disappoint, boiling down Mitt Romney’s case to one sentence: “In Tampa,” Clinton said, “the Republican argument against the president’s reelection was actually pretty simple, pretty snappy. . . . ‘We left him a total mess, he hasn’t cleaned it up fast enough, so fire him and put us back in.’ ” He cast the philosophical differences between the parties just as crisply. Republicans, he said, believe in a “winner-take-all, you’re-on-your-own society,” while Democrats seek “a country of shared opportunities and shared responsibility — a we’re-all-in-this-together society.”

That Clinton, the cheerful political educator, played such a central role at this conclave reflected the extent to which it should be seen as a three-day tutorial designed not only to defend President Obama’s economic stewardship but also to advance a view of government for which, over the past 40 years, Democrats have often apologized.

And off Clinton went in his classic style: the “country boy from Arkansas,” who was rambling yet focused and methodical, embroidering his text with folksy asides, getting the crowd to cheer even budget numbers and statistics. He went long, and they wanted him longer.

It’s ironic that the 42nd president played the co-professor with Obama in this advanced government class. Clinton is associated with a determined effort to distance his party from its past, and when he pronounced in 1996 that “the era of big government is over,” it was taken as a concession to the new conservatism that swept to control of Congress just over a year earlier.

But Clinton’s rhetorical move was more tactical than fundamental. He never stopped believing in the power of government. And with Republicans putting forward the most emphatically pro-business, anti-government agenda since the Gilded Age, Democrats feel an urgency to assert the state’s positive role. Thus, one of the most applauded lines of the convention’s first night came from Massachusetts Gov. Deval Patrick: “It’s time for Democrats to grow a backbone, and stand up for what we believe.” Rarely has a party so fully embraced a declaration that implied its own past spinelessness.

Clinton, once known for the strategy of “triangulation” between the parties, was among the speakers who answered Patrick’s call. He assailed Romney and Paul Ryan for falsehoods on welfare and Medicare, dismantling one Tampa argument after another. Offering a vision of “shared responsibilities, shared prosperity [and] a shared sense of community,” he stoutly defended Obama’s health-care law, student loan reforms, rescue of the auto industry, commitments to community colleges and job training, and budget proposals.

He joined Elizabeth Warren, the financial reformer running for the Senate in Massachusetts, in presenting government Wednesday not as an officious meddler in people’s lives but as an ally of families determined to help their children rise. Government, Warren said, “gave the little guys a better chance to compete by preventing the big guys from rigging the markets.”

And there lay the other stark contrast between the Tampa Republicans and the Charlotte Democrats. Building their convention around an out-of-context quotation from Obama, Republicans offered a counter-theme, “We built it.” But the message of Tampa often came off more as: “We own it.” Working people and the dignity of labor receded into the shadows cast by the investors, entrepreneurs and business leaders.

The Democrats’ version of the American dream is built of different stuff, on individual and family struggle. Republicans may cast themselves as champions of “family values,” but Democrats here — notably Michelle Obama and San Antonio Mayor Julian Castro — spoke far more about upward mobility as a family enterprise.

Yet Democrats know that the president still carries the burden of high unemployment and sluggish growth. And that is why Obama called in as a witness the man who presided over years that voters remember as an all-too-brief journey through the economic promised land.

Obama, Clinton testified, “inherited a deeply damaged economy, he put a floor under the crash, he began the long, hard road to recovery, and laid the foundation” for a new economy whose positive effects they would soon feel. “With all my heart, I believe it,” he said, devoutly hoping that his heart-to-heart talk would get Americans to believe, too.