Former Nixon aide a source of left-wing bias?

Diane Sawyer as press aide shortly after Watergate.
Source: www.whitehousemuseum.org
/west-wing/press-secretary.htm 

The interview between Jon Stewart and Chris Wallace on Fox News has drawn quite a bit of attention (if you have not seen it, it is here). While everyone seems mainly focused on Wallace's admission that Fox intentionally tries to go far right to counterbalance the perceived left-wing bias in the rest of the media, I found another aspect to be peculiar.

One of the examples that Wallace gives of left-wing media bias is the way Diane Sawyer presented a particular issue. Stewart does not point it out, but Diane Sawyer is a peculiar choice for a source of left-wing bias. She started her career as a Republican press aide and worked as a "literary assistant" (as Wikipedia puts it) to Richard Nixon – after Watergate and even after his resignation.

I don't know if Sawyer has changed her political stance over the past 35 years, but I could not find any indication that she did so in a quick search online. If she remains a Republican supporter, then she is surely a poor example of a source of left-wing bias.