Against what threat, rh200? Trident can't deter ISIL, stop Russia going into Crimea or sort out the Taliban.
Its not about the threats we have now, or any other half baked ones. The fact is, we seem to think things get easier, they don't they get harder. Having an arsenal that can keep things to low level conflicts is imperative if we want to stop having wars between the major players.
By wars amonsgts the major players, I'm talking about world wars, with the death tolls in the tens if not hundreds of millions. In effect, it just regulates us to what we have now, pain in the @rse conflicts.
The problem being, the Yanks seem to be on shaky ground, and I'm not sure how long they can be relied to be the foundation of our defense. This is where the problem comes in, what does the modeling show if the yanks are taken out of the equation.
Human nature dictates that when there is a power vacuum there will be a stampede to fill it. So the question becomes, do you have enough deterrent to make it hurt enough, so that another larger player will leave you alone? Factor in, the potential that other major player may control their media and are prepared to loose a city or two?