1 Corinthians 11:27-29 Therefore whoever eats this bread or drinks this cup of the Lord in an unworthy manner will be guilty of the body and blood of the Lord. But let a man examine himself, and so let him eat of the bread and drink of the cup. For he who eats and drinks in an unworthy manner eats and drinks judgment to himself, not discerning the Lord's body.
Neither the sin of the recipient nor the minister diminishes the presence of Christ in the eucharist. Rather, it diminishes the efficacy of that presence toward the sinner, perhaps even reversing it so that a blessing becomes a curse, yet the presence is not to be doubted.