Well not ALWAYS. McNabb led the Eagles to five NFC Championship Games, but he also had a few really bad games too.
Statistically speaking, McNabb has played worse in December only three times in his career. But McNabb's 68.0 quarterback rating is his worse in this month since 2004.
McNabb's stat line for today? He completed 26 of 44 passes with one touchdown, one interception, and one lost fumble. The quarterback was also sacked four times. If not for Anthony Armstrong, with his 97 receiving yards and one touchdown, McNabb's numbers would have looked even more awful.
The news doesn't get any better. As poorly as he played, this wasn't even McNabb's worst game of the season. His quarterback rating was lower in games against the Cowboys, Eagles, and Bears. All games that the Redskins won.