Median voter theorem and Senator Specter

Hotelling's Law says that two profit-maximizing hot dog vendors on a beach will both put their hot dog carts in the middle of the beach... and it also says two vote-maximizing political parties will both target the middle of the political spectrum because of what's called the median voter theorem: Whoever gets 50% of the votes plus one wins. Or, to quote the Oprah Winfrey show from September 2000:

WINFREY: You don't care what other people think about you?

BUSH: Well, I care what 51 percent of the people think about me.

The challenge for political candidates is that primary elections are usually only held on one part of the beach, i.e., Democrats on the left side of the beach, Republicans on the right; hence the desire by candidates to "move to the center" after they win the primary election. And hence the decision by PA senator Arlen Specter to switch from the Republican to the Democratic party after determining, in the words of the NY Times, that "he could not win a Republican primary against a conservative challenger, particularly in light of his vote for the president’s economic stimulus package."

The op-ed by moderate Republican senator Olympia Snowe is also worth reading.