I think they'd just threaten to keep the laptop instead. Once they've taken the laptop from you, presuming that's the only reason they're stopping you, they should no longer have cause to prevent you from continuing.
In any case, if you are worried about protecting your data, you put yourself in a pretty bad situation if you rely on encrypting that data and hide the password. Bringing a relatively clean laptop will just avoid the issue altogether and will allow you to be cooperative with them.
Remember that they don't _need_ any cause to deny you entry or detain you, as long as you're not a US citizen.
Because messing with you is equally rewarding as "protecting the country."