Just read the law. I'm not sure what it means for Sanders to invoke the act. The way I read it, it should have automatically applied. Congress would likely have to sue the Biden administration to force them to comply.
That said there's a get out of jail clause. Basically, Biden simply needs to write a letter with his excuse for ignoring war crimes. it'll go "something something Oct 7 gives Israel the right to genocide".
And that's it, aid flows freely after that.
Still, at least Bernie is raising this as an issue.