Sen. Rockefeller, 75, is completing his fifth term in the Senate, continuing to be elected as a Democrat despite West Virginia becoming more and more of a Republican territory in its statewide elections. The announcement puts into play a seat normally regarded as a safe Democratic hold due to Rockefeller's tenure and ability to bring home pork - a feat learned well from Robert Byrd, who represented the state for over 50 years in the Senate himself.
Even Rockefeller himself acknowledged it may be a hard seat to hold now for Democrats, but stated, “It’s not a part of this. It was easy enough not to have to worry about that.”
Several factors, though, point to it possibly being a tough race. West Virginia has voted Republican in every presidential race since 1996. Rockefeller's enthusiastic support of Obamacare would make him a likely target. Lastly, popular Rep. Shelley Moore Capito (R) has already declared for the race. With this announcement, though, a flip is much more likely.
And with this announcement, the 2014 campaign season has begun in earnest.