Senate Democrats fear new START treaty could 'blow up'

I wouldn't worry too much.
China has already stated that they won't play ball with this treaty (which they are not a signatory of) and both Russia and the USA are busy developing weapons not subject to the treaty.
It is not like the Russians have the money to build a whole new strategic force, and even if they did, all that would serve to do is make the rubble bounce.
The real threats are space-based, cyber, and hypersonic and enduring continuously airborne weapons.