In terms of biggest need I think top 4 LD is probably it. Orpik has been getting 2LD minutes and has been absolutely hammered in them: to the tune of 44% of the shots and only 40% of the goals (both worst amongst the 6 regular D) while not even drawing the toughest deployments. And it's not like he's had a sterling playoff reputation in recent years to fall back on either. He needs to be pushed down or out of the lineup, and while I like Djoos quite a bit I'd much rather have him playing third pairing minutes in the playoffs instead of 2LD minutes.
I mentioned it in another thread and while McDonagh would be the big catch in terms of LD acquisitions, I think it's unlikely the Capitals and Rangers could make a deal.
On the other hand I think Oscar Klefbom could be an interesting target if he's made available by Edmonton. He's had a poor season in terms of results but his underlying numbers are still quite strong and I'd bank on his results turning around quickly. I think it could be a fit because Edmonton is in desperate need of wingers and they could be tempted to take Burakovsky and try to rekindle the McDavid/Burakovsky junior connection. Klefbom is young and under a team-friendly contract of $4.167M/year for 5 more seasons and it would allow the Capitals to deal one of their LD prospects (Johansen, Siegenthaler) as a pot sweetener to acquire Klefbom since that is a rare position of organizational strength for Washington (Orlov, Djoos, Johansen, Sigenthaler). I'd want a rental winger back in return if I'm Washington to replace Burakovsky, maybe Maroon.
I wonder if something like Burakovsky + Johansen/Siegenthaler + (Washington's first rounder or Florida's 2nd rounder) <--> Klefbom and Maroon (retained if necessary) wouldn't make sense for both sides.
I think the Capitals need to be bold this TDL. They only have a few more shots with Ovechkin and Backstrom before it'll become necessary to begin a rebuild. I think they need to be aggressive and worry about the future in the future. The Metro is weak this season (aside from Pittsburgh) and it's as good an opportunity as any to go all in. It'd suck to give up assets but they have plenty of valuable veterans they can deal in the future to restock the pipeline (Niskanen, Ovechkin, Backstrom, Holtby).