Several months ago, Politico noted that many Republican voters, especially in the activist base who’ll help choose the GOP presidential nominee, “have a dark, foreboding feeling that America is in decline.” Leading Republican candidates are keenly aware of these attitudes, and will be eager to speak to these voters’ sense of dread, “tailoring their rhetoric to tap into a fear that is apocalyptic in tone.”

That was in March. Nearly six months later, the GOP field has no use for hope, and has decided to push a message of dread and dismay.

Looking for a bit of optimism about the future? Hoping for a quick psychological pick-me-up amid the economic downturn? Don’t tune in to the Republican presidential candidates. As they reach for the sharpest contrast they can find with President Obama, the Republican presidential hopefuls are sounding anything but hopeful. On the trail, they are painting an increasingly gloomy picture of the nation they want to lead.

I haven’t the foggiest idea how this resonates with the American mainstream. On the one hand, the public is frustrated and in a deeply sour mood. It’s not unreasonable to think miserable voters might connect well with candidates who speak of nothing but misery. When folks are depressed, do they want to hear about optimism and sunshine?

On the other, it seems at least as likely the public may not want to hear would-be leaders wallowing in despair. As the NYT‘s Michael Shear noted in his piece, “Too much talk about gloom and doom could turn off voters who are tired of feeling worried…. It’s easy to fill a stadium full of excited supporters with a rallying cry that suggests things will get better. Wooing supporters with depressing news is a tougher sell.”

This could prove to be an interesting angle to the 2012 race.

Whenever this subject comes up, the conventional wisdom generally tells us we’re supposed to think of Ronald Reagan, since “optimism” was a key element of his appeal. It was fundamental, we’re told, to understanding his entire persona — the former president had an infectious, unyielding optimism.

I tend to think much of this 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.”

I wouldn’t be surprised if President Obama tried to take advantage of this, too. In his debt-reduction speech in April, he took on Paul Ryan’s House Republican budget plan from a variety of directions, but he specifically noted, “I believe [the Republican plan] paints a vision of our future that is deeply pessimistic.”

It’s a compelling charge. Not only are Republicans miserable about the present, they’re also presenting a dour vision of the future, with the elderly, low-income families, students, small businesses, and struggling communities all 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.”

If an underlying theme of the 2012 race is optimism vs. pessimism, I suspect President Obama would welcome the campaign dynamic.