Oh, it was a terrible trade, but Caps fans don't care about it as much anymore.
In any event, had they not traded him, three or four subsequent moves would not have happened, without which the Cup win might not have happened. Certainly they would never have been able to ice the same team. They built a team full up to the gills on the salary cap without him, and they relied on their depth scoring to win.
Beyond that, they can't exactly fire their GM again, and GMGM has now suffered enough for his transgressions. They've won a Cup before Nashville, and before GMGM, both of which help a great deal.
Basically, Caps fans are feeling no pain this summer.