The recent history of these things is that the party-switcher ends up landing in the mainstream of his new party. But in Specter's case, with the Democratic Party already coalescing around him and asking for little in return, that may not be so. In his press conference, Specter said he would retain seniority inside the Democratic Party and would therefore be likely to possibly earn a committee chairmanship in the next Congress. Harry Reid seems to have given up way too much to earn Specter's place in the caucus, considering that he was a goner if they refused. He also announced that he would oppose President Obama's nominee for the Office of Legal Counsel, Dawn Johnsen. He may have an emphasis on some other issues, but basically he's going to be the same, probably demanding certain changes on key legislation to befit his moderate heart before invoking cloture. For instance, he may have to make some grand compromise on Employee Free Choice in order to show his bona fides to labor and a Democratic primary electorate. But whether he guts legislation from the Republican or Democratic side of the aisle, Washington will continue to revere him. Hell, Obama said today he'd campaign for him.
For his part, Rep. Joe Sestak said he'd still entertain a primary if Specter doesn't hew his views closer to the Democratic Party. Good for him, though he'll have lots of pressure to stay out.
Sen. Joe Lieberman (Democrat-turned-Independent Democrat, Connecticut) put out this statement welcoming Sen. Arlen Specter (Republican-turned-Democrat, Pennsylvania) to the Dem caucus:
"I enthusiastically welcome my good friend Arlen Specter into the Democratic caucus. It will be very good to have the company of yet another independent minded Democrat in the caucus!
"I have always admired Arlen as a man of deep principle who has been a bridge builder to get things done in the Senate. Arlen understands that we get things accomplished when we listen to the vital center of American politics. I know that Arlen will continue to make a major contribution to the Senate and the nation as an effective independent leader and problem solver."