Why was Kerry doing so bad in the polls before the first debate

[PragmaticPopulist]

Kerry was leading until the RNC Convention.

Bush was leading bigly after the Convention but the debates damaged Bush and narrowed his lead because he did terribly.

The 2004 RNC lasted from August 30th to September 2nd, here's the aggregate polling before the Convetion:

http://www.electoral-vote.com/evp2004/aug/aug29.html

Kerry was leading with 270 electoral votes, and here's the aggregate polling after the Convention:

http://www.electoral-vote.com/evp2004/sep/sep03.html

Bush 270 Kerry 252

Didn't know Tennessee was on the radar of competitive states in 2004. Was it because of the common polling error in Tennessee of overestimating the D vote? Or was Kerry definitely favored there at one point during the campaign?