As a Bruins fan I wouldn't make the trade but, it seems pretty likely that's what it will take to acquire Trouba.

Pass. Krug for Trouba is a lateral move.

Well yes and no. It's shifting a LD asset into a RD asset. It makes getting a RD less necessary when you try to add an additional top 4 D, like say Fowler. Instead of Chara, Fowler, Krug, Liles, Ehrhoff all on the left and Miller, Miller, and McQuaid on the right. So while yes Krug for Trouba is in itself Lateral it opens more options to add another top 4 D.

While on the surface it seems like a lateral move especially when factoring in Krug's advanced metrics, Corsi, etc...the difference is Trouba can and has logged heavy penalty kill minutes while Krug is limited due to size. It may also be easier to replace Krug's production on the PP with a specialist like Liles or now Ehrhoff if he can continue the resurgence. They also had Zboril, Luzon, Grzelcyk, and O'Gara coming up as LHD. I personallly like Krug as a heart and soul player and would not make the move for the mercurial Trouba.