Suzy Khimm examines it:
Political parties have good reason to embrace party-switchers: Aside from the PR boost, party-switchers fairly reliably change their votes to reflect their new parties’ views, as political scientists Nolan McCarty, Keith Poole and Howard Rosenthal have found. But the general public is more suspicious. “Voters punish members who switch parties,” Yoshinaka writes in a 2011 paper he co-authored with Christian Grose. “On average, switchers lose about seven percentage points in all elections after they switch.”
Sean Sullivan recalls famous political defections.