Romney isn’t a Republican so it shouldn’t be applied to him. Everyone should attack him.
Many politicians who run on the Republican ticket have, at the core of their political identity, a desire to "work with" the Democrats. Were Democrats to be thoroughly discredited, such politicians would lose their raîson d'être. They will thus fight to ensure that doesn't happen, and will work to undermine what should be the Republicans' strongest weapons against the Democrats. Victory against the Democrats is not going to be possible without first vanquishing such RINOs within our midst.