I doubt even a Republican would be willing to lower corporate income taxes. Nominal rates haven't been touched for quite a while; politicians opted instead to just allow the loopholes and safe havens to continue lowering the effective rate, and corporations seemed to be happy about that.
The likely reason for corporations holding onto cash is the lesser impact deferrals can make in today's markets. Companies are becoming larger and larger umbrellas every year, and as the need to hire new people presents itself, the unfortunate realization for them is that they must look to the bigger cities for their best talent. NYC, LA, SF, DC, etc., are the best places to acquire talent, and they are also home to some of the highest tax rates in the country.
This makes talent acquisition increasingly expensive, and that means less money that can go to the offshore safe havens that allow deferrals to be so lucrative for companies. So, companies hire as little as possible, and though corporate revenues are decreasing rapidly as a result, it's better for them than having to face a rather unstable business environment in the US, where all your massive infrastructure and talent investments may be useless in just a few years' time.
I believe that the US is becoming increasingly unfriendly to businesses, and the lack of political cooperation in DC is showing executives just how true that reality is. My contention is that businesses are holding onto cash because they may need to make sudden and quick moves in the near-future. They will either make huge hiring moves and will build out massive new infrastructure to support it -- or they will GTFO of the US while they have the chance.