They can threaten it, but there really isn’t any other currency that makes sense. Perhaps selling to China directly in Yuan does but that doesn’t really hurt the US. No one outside China trusts trusts the Yuan more than the dollar, especially given the delay in releasing financial reports last year.  Everyone else depends on a currency with enough liquidity, so the only other reasonable choice is the Euro. Considering how strong the dollar is and will likely remain for the next few years, I’m not sure why the Euro would be preferable. If the Euro or Yuan don’t make sense, I don’t see how any other currency other than the dollar makes sense.
Sadly for Britain, Brexit has killed the pound. What a mistake that was.