One can argue that those representatives who claim to be fiscally conservative but vote for unfunded liabilities are not, in fact, fiscally conservative.
You can't say "you're not a scotsman because I don't like your actions or opinions". You can say "you're not a scotsman because you're neither from scotland, nor have any particular tie to it."
Similarly fiscal conservatism has an actual definition, and it's totally vaild to say "you don't adhere to the definition", as long as you're not applying spurious constraints.
It's a political party. If people that identify X vote for you, who identifies X and votes in a block with other people that identify X for matters that attract Identity X voters to said party... then you don't get to pull the No True Scotsman. You are the party of X, whether or not some arbitrary philosophy party X is supposed to uphold is consistent with the party's actions.