These sort of concerns about National Guard units being too tied up in foreign deployments to do state-oriented disaster relief and so forth constitute the best rationale I can think of for the belief that the Army needs to get bigger. One could use a larger regular Army in order to curtail the need to call on Guard units and thereby increase domestic disaster preparedness. On balance, though, that would have to be an incredibly cost-ineffective means of addressing natural disasters, so I don't see the argument carrying the day on the merits.
Has John Edwards specifically come out against the larger military? Obama and Clinton are for it, and Kerry/Edwards endorsed a version of this idea back in 2004.