300-odd weapons does not, in any way describe their size, possible use or disposition. However, 300 is a significantly large arsenal, especially when tied to means of delivery that are precise (I know, slightly oxymoronic) and difficult to intercept, especially by potential 'rogue states'.
The current US arsenal, drawn from OS, apaprently contains many obsolescent free-fall weapons and other devices, simply held for parity purposes with the Russians. Whereas we in the West rarely think about the strategic impact of nukes, just spend a few days in Moscow speaking with Defence and Foreign Ministry officials (as I did 18 months ago) and one will soon realise that nuclear parity means everything. A constant thorn in the Russians' side are the independent arsenals held by the UK, France and, err, NATO.
In sum, the risk in reducing the US arsenal is not Russia (or any other state, for that matter - as there is enough to go around) but it is the political damage that Barack Obama will inflict on the liberal polity. The Republicans will milk this for all it's worth. Not only is he accused of being a foreign-born Muslim (he is not) he will now be accused of being a 'Commie Spy'. You just need to see some of the risable stuff from teh New American Institute and other 'Right thinking' bodies to feel just a little bit uncomfortable. Now Dr Strangelove, where were we?