Seems to me that unnamed US official is more representative than assumed, but they probably don’t want to taint the debate too much. Having Americans say no to something lead many recalcitrants in Europe to want it just for that reason.
Trident is based on the UK seeing itself much more divorced from the world around it than it actually is. What value does trident bring above and beyond the nuclear forces of the US and France? Would it ever need to be independently used from these allies in its decades of deployment? And what about the forces that have been culled to keep trident an option, what if they had received the sort of funding that would have been freed if trident had been shelved?
The UK is never going to have to use trident, and even for the purpose of posturing it is an extremely expensive deterrent. A naval strike group based on a capable aircraft carrier (capable meaning F35C) would cost much less, albeit maybe not in long term maintenance (would provide for more jobs though), and would be able to assume a day-to-day role in underwriting the global order, something that is much more useful today. It would also be a much more visible sign of Britain’s presence, interests and alliances. It would ultimately be much more useful as a deterrent too. For that reason one would think Argentina would much prefer the UK upgraded trident.
Alternatively, one could greatly strengthen the sort of capabilities that were needed in Libya or that could be called upon to help in Syria with just a portion of trident’s budget. Right now the alliance outside of the US doesn’t have much in assets that could be useful to Turkey and other Syrian neighbours if the Assad regime were to fall. Special forces, intelligence gathering, heavy lifting, refuelling, AWACS, liaisoning, Royal Marines, fighter jets. Just imagine how far £20bn takes one when investing in such assets.