Currently we just ignore invalid txs sent in the mempool since an honest peer could send txs that are invalid according to our local mempool state.

However some txs may be invalid no matter what the state, like invalid encoding, and perhaps invalid signature (though careful with how you define signature).

Perhaps we could consider punishing peers for sending us txs that are invalid in this way by making better use of standardized ABCI codes.

This was brought up in #2175