This, frankly, is pretty big news for Seahawks fans, as Jennings has been a lightning rod of controversy these last few seasons. The Kelly Jennings argument was split into two camps -- one that essentially has him cast as the scapegoat for every defensive failure (ok, that's hyperbole, one side believes he is not a good cornerback in the NFL), and the camp that thinks he still has the skills and coverage abilities to play a key role for this team. Regardless, that argument can mostly be put to rest now that he has been dealt to the Bengals.
As for the Seahawks organization, the trade is surprising after their controversial decision to re-sign Jennings, but makes sense from a team that is deep at cornerback... well, deep in cornerback prospects anyway. They don't have a lot of experience at the position, but a few players have done well for themselves in the preseason. The Seahawks are in need of depth at defensive tackle and the Bengals are in need of cornerback help after their star CB Johnathan Joseph signed with the Texans this offseason.
Cincinnati gets a solid coverage cornerback with speed but few ball skills. In his five seasons with the Seahawks, Jennings only managed to pick off two passes, and was often targeted by opposing teams' offenses. In return, Seattle gets an obscure yet intriguing defensive tackle that will likely add depth at the 3-tech position. McDonald was the Bengals seventh round choice in 2009 out of Memphis, and at 6'2, 297 and 24 years of age, will hopefully develop into a key role player for the Seahawks. The information out there on McDonald is sparse at the moment, but check back at Field Gulls for a more detailed scouting report later today.