At issue is whether a demoralized Republican Party should be emphasizing breadth or depth in terms of ideology, messaging and geography.
On one side stand the fiscally and socially conservative purists -- party activists and elected officials who maintain that Republicans need to adhere to strict principles to emerge as a strong opposition party.
Their reaction to the Specter move was summed up by conservative blogger Michelle Malkin: "Don't let the door hit you on the way out."
On the other side stand the beleaguered Republican moderates, the dwindling number of blue-state GOPers and -- less quietly -- key members of party leadership on Capitol Hill.
They maintain that the party can't afford to cut itself off from any blocs of voters, not with a popular Democratic president in office. They warn that the wrong moves now will consign the Republican Party to a prolonged minority status, chasing a shrinking base in ever-smaller portions of the country.
"There is no plausible scenario under which Republicans can grow into a majority while shrinking our ideological confines and continuing to retract into a regional party," Sen. Olympia Snowe, R-Maine -- now one of only three Republican senators from the Northeast -- wrote in the New York Times on Wednesday.
Specter's situation, of course, is unique. He was a moderate senator whose state has grown increasingly Democratic over his three decades in the Senate.
A conservative challenger seemed almost certain to defeat him in next year's Republican primary -- leaving a party switch his only real hope of retaining office.
Specter acknowledged as much in his decision to become a Democrat. But in leaving the GOP, he bemoaned what he described as the party's conservative shift: "Since my election in 1980, as part of the Reagan big tent, the Republican Party has moved far to the right."
Specter's defection has huge potential short-term ramifications. With the expected victory of Al Franken in Minnesota, Democrats now stand on the verge of securing 60 Senate votes -- enough to cut off any GOP filibuster.
But some in the party say they're not sorry to see Specter go. Not having a moderate like Specter -- who supports abortion rights and was one of only three GOP members of Congress to vote for the president's stimulus package -- makes it easier for the party to present a united front in opposing Obama.
"I'm happy not to have an Arlen Specter -- a potential traitor at all times -- who can sink Republican messaging because of his ego," said Rick Wilson, a veteran Republican consultant. "He's not a guy who was here for the good of the team."
Obama remains extraordinarily popular in polls as a smaller portion of voters say they consider themselves Republicans. But voters are expressing concern about runaway spending and deficits -- leaving fiscal conservatives convinced that the way to regain voters' trust is through adhering to a strict message of fiscal discipline.
The recent "tea party" protests against the president's tax and spending plans offered a glimpse into the potential political power of government spending as an electoral issue, Wilson said.