Before you count out Bob Corker, keep in mind that most people in the know around here have all but conceded the nomination to him because of money. Corker has already raised 3 million and this is all before he writes himself a nice fat multi-million dollar check. And as if he already didn't have an advantage, Corker also picked up Tennessee's best fundraiser, Kim Kaegi.
I do think that kind of talk is very premature as we haven't really seen a campaign yet, despite the fundraising. Bryant will throw everything, perhaps including a kitchen sink, at Corker and may very well make something stick. They're spreading a rumor that Corker is pro-choice around now and I'm getting all kinds of IM's saying "Did you know Bob Corker was pro-abortion?"
The campaign has only hardly begun and Corker hasn't spent a dime yet, so I wouldn't put too much stock into the primary polls until the respective machines get into high gear.
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.