Blue is not only the political color of the Commonwealth - it's also the mood of suburban Republicans. They're wondering what enabled the Democratic Party to take the lead in registration in both Bucks and Montgomery Counties, and to possess a majority when combined with independents in Chester and Delaware Counties.

Theories abound. One holds that it's simply the old story of voters' leaving Philadelphia for suburbia and taking their registration with them. I don't buy it. That was a partial explanation for some shifting patterns from the end of World War II until the 1970s, but not now.

According to U.S. Census statistics, Philadelphia's population slide began in the 1950s, and the city lost almost 123,000 residents between 1950 and 1970. In those 20 years, the four suburban counties (Bucks, Chester, Delaware and Montgomery) added a combined 846,138 residents - a 79 percent increase - obviously consisting of far more than displaced city-dwellers. That flight grew in the 1970s, when more than 260,000 left the city.

But by the '90s, the city's losses began to slow. Between 2000 and 2006, Philadelphia lost 69,156 residents. The four suburban counties, meanwhile, added just 104,904 - an increase of 4.5 percent. Bottom line: Since the 1970s, the city has lost progressively fewer residents with each passing decade. And while the suburbs continued to grow through the 1980s and 1990s, the rate slowed almost by half between 2000 and 2006. So there must be a more complete explanation of the GOP decline outside the city.

GOP ideologues are arguing that the registration loss in the suburbs is attributable to the party's straying from its conservative principles. "We must return to our roots," I have already heard from more than one. But I discount this theory, too. George W. Bush ran on a distinctly conservative platform in 2000 and 2004, but did not carry the suburbs in either cycle, and consequently, he lost the state. No recent candidate could embody purely conservative principles more than former U.S. Sen. Rick Santorum, but he was defeated decisively by Bob Casey Jr. in 2006.

It's not that the party isn't conservative enough to win the suburbs; it is that the party is too conservative and has lost touch with a suburban constituency.

Fault for that lies in the party's national image. Impressions of political parties are established nationally. People don't usually join a political organization based on their sense of the county commissioners, the competence of the row officers, or the performance of the borough council. They choose the party whose platform, they believe, most closely resembles their general views. And

those

platforms flow from the federal level. They are personified by national players.

In Washington, the GOP has been on the wrong side of many hot-button issues. As these issues have unfolded - the war in Iraq, Terri Schiavo, global warming, stem-cell research, and the ever-present issue of reproductive choice - the Democratic Party has made strides in the suburbs. Instead of listening to its more-moderate voices, the GOP has instead concentrated on stoking its hard-core base - a minority of Americans - by taking time out of the legislative schedule to posture on issues such as same-sex relationships.

That may play in Lititz, but it doesn't wash in Lower Merion.

That's why Al Gore and John Kerry did so well along the Blue Route, just across City Avenue, or north of the Pennsylvania Turnpike, in traditionally Republican strongholds. Some Republican suburbanites have been alienated and have left the party. Others who might have joined are not doing so.

There is evidence of a similar shift among local politicos. Last week, the state House of Representatives voted on a measure that would require handgun owners to report missing or stolen weapons, and nine suburban legislators defied the NRA by supporting it. In November, Democrats captured five of nine Montco row offices. These things would have been unheard of just 20 years ago.

And the situation could grow worse for the GOP. Take the case of U.S. Sen. Arlen Specter, who barely survived a primary challenge on the right from Pat Toomey in 2004. Specter has already announced his intention to seek an unprecedented sixth term in 2010. If he needs to fend off another primary challenge in that cycle, he will have to do it with far fewer moderate Republicans in the Philadelphia suburbs, a key constituency for him in years past. Many of those who enabled him to defeat Toomey are now Democrats. They were his margin of victory. And these changes could make it difficult for the next generation of moderates to emerge.

As Specter's son and adviser, Shanin, told me: "The national Republicans have spent too much time pumping the base, while the Democrats talk to the country. People notice. And with 81 percent of the nation saying we're on the wrong track, it'd be hard to find a county in Pennsylvania where people are happy with the national Republican Party."