Most interesting parts of US government will buy and consume software written in C++ without qualification or reservation for the indefinite future. People are wishcasting, it isn’t a serious risk. New systems are being planned in C++ today and language choice isn’t even mentioned. Parts of government have a lot of experience with C++ in high reliability contexts.
There are many advanced systems in government written in C++ that would be impractical to deliver in any other language even if you were starting from scratch today. Extreme data intensity and throughput requirements are actually causing systems written in memory safe languages like Java to be replaced with C++ systems currently. Rust is often not a good fit for the software architectures required unless you are comfortable writing a lot of awkward unsafe code.
The government is pragmatic about programming languages, not ideological. They use both Rust and C++ in new systems but not for the same purpose, both have unique strengths in certain roles that ideologues are loathe to acknowledge. I use Rust and C++ the same way.