As the Democrats gather for their national convention this week in Charlotte, N.C., the conventional wisdom is that President Obama needs to look forward rather than backward, he needs to offer a vision for the future rather than rehashing the battles of the past.

It seems like an obvious piece of advice. And yet the Republicans have tried to lure him into a discussion of the past by asking the question Ronald Reagan asked in 1980: Are you better off than you were four years ago?

The state of things four years ago will not decide this election. But, since they asked, Republicans deserve an answer, and as the convention warms up, a glance at recent history might shed light on what we might expect over the next four-plus years.

Four years ago, after eight years of Republican governance, the nation’s financial system was in meltdown. It wasn’t just the United States. The world economy was teetering on the verge of a new Great Depression, with all the cataclysmic possibilities that full-scale economic collapse can produce. John McCain doomed his candidacy in the presidential race when he asserted that the fundamentals of the economy were “sound.” He said it even as major banks were collapsing, and job losses were accelerating. By the time Obama was sworn in, the nation was losing 800,000 jobs per month.

The Bush administration had leaped into the breach to prevent the banking system from collapsing. Congress passed and President George W. Bush signed the Troubled Asset Relief Program, known as TARP, and widely reviled as the Wall Street bailout.

At that point the nation had fallen victim to a vast pattern of irresponsible behavior, crime and misjudgment by both business and government. Wall Street magicians thought they could manufacture wealth out of thin air; the thin air turned out to be shoddy loans and fancy financial instruments that constituted little more than a Ponzi scheme. Everyone was looking the other way, including auditing firms and rating agencies, including the government. Alan Greenspan, once hailed as “the maestro” of the Federal Reserve, was moved to admit that the self-regulation of banks did not take into account human greed. Oops.

Obama saw at once that the economy needed a major jolt, and he put together a stimulus program that was criticized by some as too small and by others as too large. Even so, the private sector was paralyzed, and government spending was the only way to prime the pump. His stimulus and other measures, such as the auto bailout, saved millions of jobs.

Republicans at the time faced an existential crisis. Everything they stood for was in danger. Eight years of George W. Bush threatened to cast Republicans into oblivion for the foreseeable future, as they had been upon the election of Franklin Roosevelt. Obama, too, saw it as a Roosevelt moment, and he proposed an array of public works initiatives as part of his stimulus package.

How, after all, were the Republicans going to argue against stringent new regulation of Wall Street or against an economic rescue package? Their credibility was in shreds. In order to avoid long-term exile, they decided on a bold strategy: Oppose everything Obama does, no matter what, and ensure that he fails. If the economy flounders, the voters would turn to them to rescue the nation from Obama’s failures. Obama’s appeals for bipartisanship were answered by a determined effort to sabotage his best efforts.

This is all ancient history by now, and Obama can’t dwell on it as he makes his case for another four years. Yet somehow the people need to be reminded of everything he has been contending with and all that he has accomplished. One reason is that Mitt Romney is promising more of the politics that produced the inequality and disaster that were the legacy of the Bush years.

The past is relevant, if not determinative. Obama can build on that past to offer us a future that promises much more than the gloom and doom purveyed by the Republicans. He can summon us to the greater challenge of fulfilling the nation’s vast potential. He will find the American people hungering for his call.