Here's an interesting chart, which strongly suggests that the election of a Democratic president reliably leads to greater income gains for those at the bottom, while the election of a Republican has the opposite effect. To be more specific:

When a Republican president is in power, people at the top of the income distribution experience much larger real income gains than those at the bottom--a difference of 1.5 percent per year going from the bottom to the top quintile in the income distribution. The situation is reversed when a Democrat is in power: those who benefit the most are the lower income groups. If you are in the bottom quintile, the difference between having a Democratic or a Republican president in office is an income gain (or loss) of more than 2 percent per year! Strikingly, compared to Republicans, Democratic presidents generate higher income gains for all income groups (although the difference is statistically significant only for lower income groups).

Can any of the bishops who are insisting that we are morally obligated to vote for John McCain point to a similar chart relating to the number of abortions performed in the United States to the party (or views on abortion) of the president in power? Just wondering. (The chart is from a recent book by Princeton political scientist Larry Bartels.) (HT Matt Yglesias)UPDATE: While not a response to my question, this thorough post over at Public Discourse makes the argument for the difference pro-life politicians have made. While I think the argument the post makes is basically sound, I wonder whether it can support the notion that the election of any particular politician (or even president) makes, by itself, such a dramatic difference on abortion that any particular politician's views on abortion should trump all other issues (and the likelihood that the politician might make even more progress on THAT issue) in deciding how to cast one's vote. Just to be clear, my point is not that a candidate's views on abortion will not have any impact on progress on that issue, but simply to question whether they will have such an obvious, immediate, or predictable impact that it is possible, as some are (again) attempting to do this year, to use the gravity of abortion to attempt to compel Catholics to vote for one particular candidate or party.