I'm not worried about the defense. To me, Gudas & Jensen are decent enough, especially given what they are paid.
The Caps have invested heavily in the forwards, and for this team especially, in playoffs almost everything invariably comes down to how much the forwards can tilt the ice on the forecheck and in the neutral zone, how many of those 4 lines are outskating or at least keeping up. If they are mostly taking it to the opponents, this defense should do fine. If they spend significant time on their heels, the odds drop so drastically that any trade to improve the defense (especially of the stay-at-home type) will be pretty insignificant in comparison, IMO.