Senator Specter's decision is a continuation of what we have seen across the nation -- at least since the 2006 Democratic Congressional takeover of both Houses of Congress and the substantial margin of Barack Obama's victory and further dramatic gains by Democrats in the Congress in 2008 -- the expanding strength of the Democratic Party among moderates and independents. Specter has exemplified just such a moderate and independent political profile for many years.

Today's move by Senator Specter to the Democratic Party points to the further narrowing of the Republican Party to an ideological, "just say no" conservative band that appears to be out of touch with the mainstream of the country.

Lanny Davis is a regular weekly columnist for The Hill. In 1996-98, Davis served as special counsel to President Bill Clinton. He attended Yale Law School with Hillary Clinton in 1969-70 and has remained friends with her ever since. He is the author of the book, "Crisis Tales: Five Rules for Coping With Crises in Business, Politics, and Life," (Simon & Schuster March 2013). Follow him on Twitter at @LannyDavis.