Yes Libra can be launched without any limits or hesitation by US Govt because it is owned US citizen only.
However, with intervention from US Govt, Mark Zuckerberg maybe not really sure to launch it. We all know about the power of US Govt.
Yep, The US Govt will fight to ban, but this Zuckerburg will pay huge amount to the opposition gang, anyway we have to wait and see how they move on. They didn't abonded the project and continuing till to date so we need to be patience and watch them.
We have seen how many tried to stop Bitcoin in the past and failure in this they have invested themselves.