They are clearly hoping to push legislation for a backdoor
Last time they wanted Apple to push in an iOS update that would get around the limits on trying passcodes (note to terrorists, use passwords instead of passcodes and this won't even be possible) though I'm not sure if that is still a possibility - they may have closed the route to forcing iOS updates in a locked phone in DFU mode. At least I hope they did, as there's no reason that should be necessary.
The real prize they want is a law requiring either a backdoor for law enforcement, or for Apple (and Google etc.) to not design phones that they can't unlock. Either they'd have to build in some sort of "master key" that could unlock phone (hopefully specific to a given serial number though I'm sure that's not the option a jackboot like Barr would choose) or have to ship a copy of the key created when a user sets a passcode to Apple.
I'm sure such a vast database of unlock codes for every iPhone in the world wouldn't be a hacker target, or tempting to insiders to access for fun or profit...
I wish Apple would allow for a way for a user to set an encryption key for iCloud data. Currently Apple is able to hand over iCloud data since while it is encrypted, much of it is only encrypted once and with a key Apple controls. I imagine the reason they haven't done this is to placate the FBI by providing a way to get data from most users (I don't use iCloud, I do local backups which ARE protected by a key only I control)
If the fight with the FBI gets nasty, Apple should go full privacy and offer that option for iCloud to really stick a finger in their eye. If stupid laws and politicians playing on fear are going to try to take away our privacy, I hope they go down fighting!