"I don't happen to subscribe to the notion that everybody who criticizes Tom Daschle is criticizing Tim Johnson. I think that's a bit of a stretch"

John Thune is suggesting that not everybody who criticizes Tom Daschle is necessarily slamming Tim Johnson. He thinks that it is a little a stretch to assume that the 2 are linked in this way. He is indicating that it is possible to criticize one without necessarily slamming the other. This might be because the 2 have various views on particular problems, or since they have different roles in the government. Thune is suggesting that it is important to consider the private benefits of each person, rather than lumping them together and assuming that criticism of one is criticism of the other. He is emphasizing the importance of taking a look at everyone and their individual actions and beliefs.