Gov. Chafee's declaration of dependence?

Lincoln Chafee earned a reputation in the U.S. Senate as one of that body's most liberal Republicans. Despite that, he lost his seat (representing Rhode Island) in the Democratic surge of 2006. By 2010 he most likely could not have won a Republican primary, yet he ran for governor as an independent and won. Since there were seven candidates on the ballot, he needed only about 36% of the popular vote to win. It's assumed that it won't be so easy next time. According to sources, Chafee has decided that the easiest route to re-election is to preempt competition from the Democratic party. Therefore, Chafee is now expected to register as a Democrat and run in the gubernatorial primary next year. The odd thing about this is that many Democrats, or Democratic sympathizers in comment threads, are gloating about this. They act as if Chafee had only just formally defected from the Republican party, treating his change of registration as a dis to the GOP. The cynicism behind Chafee's move and the Democrats' expected welcome to him doesn't seem to register as strongly. However nobly liberal he may be, Chafee may prove a master at manipulating the party system to his personal benefit. He may expect his hard-core supporters to give him an advantage in the primary, unless establishment Democrats can unite behind one candidate. Rhode Island requires independent candidates to register early, so a Chafee primary victory could preempt a serious challenge from his left, unless voters decide to take established parties to the left of the Democrats seriously. Chafee probably does come close to many people's model of an establishment liberal Democrat, but there also has to be a reason why Democrats voted against him back when he was a Republican. If the only reason was his brand, and a change of brand only will win their loyalty, what does that say about the American party system?