>Attacking a huge network like bitcoin would be an audacious and expensive act, but there are certainly organizations with the resources to do it, e.g. intelligence agencies, organized

How do you propose they would go about doing this? Would they jam up the whole worlds chip production to source the ASICs at above market rates? How could this be profitable?

Perhaps by taking over existing mining operations, but then you’d need to somehow perform the attack before you’re detected.