...There are certainly reasons why it's a workable strategy. The question now is can we afford to maintain it? How much deterrence is enough? What do we keep if we can't afford to keep it all? If it's strictly about credible deterrence, do we need 'offensive' nuke bomber capability?
All good questions, and ones folks in charge seem to be asking. I think we could draw down our nuke force a lot to about 100-150 ICBM's, 8-10 SSBN's and one type of bomber I think would be enough off the top of my head.
One reason to keep the bombers would be as 'proportional response' option as a deterrent, smaller nuke powers like North Korea wouldn't necessarily rate an ICBM if they set off a small nuke and Russia using a nuclear-tipped GLCM to take out a base doesn't mean we respond with an SLBM. I have seen it argued that Russia could be even more tempted to use a small nuke if our only nuclear response option was massive retaliation, especially since Russia uses nukes much more as an integral cornerstone of their national defense strategy than we do. Would we really risk a full-scale nuclear war if Russia nuked a few NATO bases in Poland and Romania?
Also firing either an SLBM or ICBM would also raise the alarm almost immediately to our enemies and escalate things in an instant, Russia and China would have to decide in mere minutes whether that nuke missile we just launched is headed to North Korea or them. It paints them into an almost impossible corner. Who is going to notice a cruise missile launched from the middle of the ocean?
A lot of this has to do with nuke strategy though and how we would intend to use nukes as a deterrent, and there has been and continues to be ample debate on that.