No, Jeff. The comments here only show that all of us tend to interpret news in self-serving ways. Had the Democrats fared better than the Republicans, which side of the aisle would be playing up the disconnect between self-reported mental health and actual mental health?
You cite Louis' letter, which describes Republicans as optimists and Democrats as gloomy. But shift your perspective a bit, and it's reasonable to make precisely the opposite case. Which party is more optimistic about the government's ability to affect lives for the better? Which party believes that we can have a country that is both safe from terrorism and a staunch defender of civil rights? Which party believes that we can engage in a respectful foreign policy, rather than bullying everyone who disagrees with us?
The Republicans strike me as hopelessly negative, whether it be their acceptance of torture, their increasingly shameless efforts to keep us angry and fearful towards our enemies by invoking 9-11, immigrant hordes, "Islamofascism," and "East coast liberals" (the rallying cry of Utah's recent attempt to pass school vouchers). The message of Republicans seems to be, "Be afraid. Be afraid of the gays, the immigrants, the secular atheists, the abortionists, the environmentalists who want to take your jobs and give them to spotted owls. But above all, be afraid of a Hillary presidency."
Either party can be spun as the party of optimism. I don't think that explains the poll results. None of the explanations offered so far really satisfy me, though a difference in introspectiveness comes close. My guess (which is probably self-serving) is that Republicans tend to be less affected by reports of suffering, not because they're discompassionate or sociopathic, but because they tend to ascribe personal suffering to the consequences of the sufferer's poor choices rather than systemic problems.
Therefore, it would make sense if Republicans were less troubled by bad news than Democrats. As someone who believes that there are severe systemic inequities in the world, such a dismissive, "I gots mine" attitude seems heartless and naive. But it might also give Republicans a feeling of greater control over their circumstances and a more positive outlook. They may also be optimistic because they compare the world around them to a world where everyone lived under Sharia law, or everyone is broke because liberals dismantled the economy and used the scrap to make hemp farms. Democrats are more prone to compare it to the more just, equitable, and sustainable world that they're hoping will emerge, and get frustrated and dissatisfied.
More grist for the discussion: a Pew Research poll indicating that Republicans rate themselves as happier.
Is it better to increase your mental well-being by turning a blind eye to suffering? Or to let yourself be dragged down by things you cannot control?