Right now, anyone – citizen or not – entering the Land of the FreeTM can be subject to warrantless probing of their electronics, which can be seized for further study in the lab for months if necessary. It’s just that citizens can’t be prevented from entering their home country: you can have your equipment taken and scanned, you can be questioned for hours, but you’re still ultimately allowed in. Foreigners, on the other hand, have no such protections: they can be searched, grilled, and sent back the way they came, if immigration officials deem you to be a problem.
The draft legislation – which is still in its early stages – is essentially designed to make it a lot tougher to stop and search citizens on the spot when they return to the US of A. However, the bill is weighed down with one major caveat. If officers have serious concerns about a traveller but have no time to get a warrant, they can seize the electronics and later apply for a warrant retroactively. If the warrant application fails, all the information harvested must be destroyed and may not be used in further prosecutions.