Probably Sekera at the 2015 deadline. I feel like that trade, and the ultimate result of that season for the Kings, it didn't force Lombardi to do it, but I think it pushed him to make the Lucic deal. If the Kings make the playoffs in 2015, I don't know if he makes the deal for him at the 2015 draft.
Lombardi protected that 1st round pick in case the Kings missed the playoffs. If they did, Carolina gets the 2016 1st. Had they made the playoffs, Carolina would get the 2015 1st. It's just my theory, but since they missed the playoffs in 2015, and then had to give up the 2016 pick, in case the Kings also missed in 2016, you don't want to win the Matthews lottery with that pick, and not get to pick him. So you do what you can to make the postseason.
If they don't make the Sekera trade, they probably have both the 2015 and 2016 picks, and then you can use them or trade them for something else. Sekera came in, didn't do a ton, got hurt, the team missed the playoffs, he went to Edmonton, and then the Kings sort of doubled down on Lucic, only to fade down the stretch in 15-16, quietly go out in 5 to the Sharks, and then Lucic went to Edmonton. For all that, the Kings got 1 playoff win, 0 players, and it cost them two 1st round picks to do it.