It doesn't really matter how much money Corker has, or even how good a candidate he is. The fact is that mayors never get elected to the US Senate. Even mayors from huge cities (Bob Anthony, Ron Kirk, Alex Penelas) routinely fail miserably in Senate runs. They just don't have the statewide network or name ID to jump right into a Senate campaign.
There are currently four US Senators whose highest previous elected office was mayor. One was appointed to the Senate (Chafee), and two were nominees for Governor before trying to pull off a Senate run (Feinstein and Coleman).
The one exception is Luger, who was mayor of Indianapolis in the early 1970's. How many mayors have run for Senate and failed since them? I have no idea, but I'd guess it was at least fifty. If you want to get for Senate, get elected Governor, AG, congressman, or state senator first.
Ron Kirk was a bad mayor (of Dallas) and an even worse candidate, just as an FYI.