A noble spirit embiggens the smallest party faction

Via Sullivan, here's Mike Tomasky's take on the danger's of a Sarah Palin presidential nomination:

The Republican primary will likely be set up in such a way that she’ll be able to pull the field, and the party, hard to the right, and while that will be fine for Barack Obama come Election Day, it will help cripple any attempt to do anything constructive afterward.

This differs from the situation today how exactly?