ESTABLISHING A TEST OF OPTIMISM…. The conventional wisdom tells us that a key element of Ronald Reagan’s appeal was his “optimism.” It was fundamental, we’re told, to understanding his entire persona — the former president had an infectious, unyielding optimism.

When it comes to Reagan, I tend to think this much of this talk is just hype and p.r., but the myth has endured to the point that it shapes coverage of presidential campaigns. The media scrutinizes contenders based on their capacity to be the “optimistic” candidate.

And campaigns take this seriously, too. In 2004, one of the first big general-election ad buys from the Bush/Cheney camp was for an ad that quoted the then-president saying, “I’m optimistic about America because I believe in the people of America.” A voice over said John Kerry was “talking about the Great Depression. One thing’s sure — pessimism never created a job.”

With this in mind, there was part of President Obama’s speech yesterday on debt reduction that stood out for me. While rejecting in forceful terms the House Republican budget plan, the president explained in some detail why the GOP agenda is callous, morally wrong, and ineffective.

But that’s not all he said: “I believe [the Republican plan] paints a vision of our future that is deeply pessimistic.”

Right. If yesterday’s speech was a battle of competing “visions” — a word Obama used 15 times — it was also a chance for the president to make clear that his rivals see a bleak and ugly future, in which the elderly, low-income families, students, small businesses, and struggling communities are left to fend for themselves.

Republicans, in other words, aren’t merely wrong. They’re also lacking in optimism and a can-do spirit. Or to borrow some cliches, Obama still believes, “Yes we can,” while his GOP detractors still want Americans to accept, “No we can’t.”

Indeed, this may become increasingly explicit over the next year or so. Politico recently noted that Republican activists, especially in early nominating states, “have a dark, foreboding feeling that America is in decline,” and GOP candidates will be eager to speak to these voters’ sense of dread, “tailoring their rhetoric to tap into a fear that is apocalyptic in tone.”

If an underlying theme of the 2012 race is optimism vs. pessimism, I suspect President Obama would welcome that dynamic and capitalize on it.