Smith.
Performance and to send a message.
Performance. I don't think that kind of message will work with a player who appears to lack mental & emotional resilience. Not a kind thing to say, but he's fragile.
Way too streaky to begin with, Smith has been protected by playing alongside Patrice, and is just not second line material. He was playing poorly before receiving the extension. If PC thought giving it to him would demonstrate confidence & result in a more secure RS improving his game, that clearly didn't happen. Julien has apparently done a lot of hand holding as well, to little avail.
That's why sitting him is the last resort.
As for Campbell & DP, good guys and once helpful cogs, they've unfortunately outlived their usefulness. That's been the case for two seasons now, and it's maddening & depressing to me that CJ continues to play them. I would move Kelly down to the fourth line and pair him with Ferlin & Talbot. Figure out the third line through various combos.