Electoral college calculus

News that the McCain presidential campaign was pulling out of Michigan (stopping its television ads, removing staff and cancelling events) hit the political world hard last week. McCain's strategists had come to the conclusion that they could not win that state and, therefore, decided to refocus their energies and resources elsewhere.

Despite the fact that Democratic presidential campaigns have won Michigan in the last four elections, the McCain campaign had, early on, believed that they could compete there this year. But with Michigan among the states hardest hit by the economic downturn, polls now show Democrat Barack Obama holding a seven point lead in that state.

With Michigan out of reach, the McCain campaign faces an increasingly difficult road ahead. Here's why:

By now, many readers, worldwide, have an understanding of the unique way Americans elect their presidents. For those who do not, what follows is a sketch of the process.

American presidential elections are not a "simple majority" wins national contest. Instead, we have 51 separate elections (one in each of the fifty states and the District of Columbia). Each state is assigned a number of "electors," with the exact number of these electors for each state being equal to the number of its Congressmen (which are determined by each state's population) and Senators (2 per state). The total of electors is, therefore, 538 - equalling 435 (the total number of members of Congress), plus 100 (the total number of senators), plus three (awarded to the District of Columbia).

Winning the overall national vote, as Al Gore discovered in 2000, does not win the White House. To win the presidency, a candidate must win the elections in enough states to amass 270 total electors (i.e., more than half of the total of all electors).