The people that poll are Catholics, baptized, Catholics that identify as and know that they are Catholic, that is why they tell people that they are Catholic, regardless of the last time they attended church.
Protestants in regard to voting are a much less vetted category.
If you identify as a Christian but aren’t Catholic, then you are put into the Protestant category, even having never been baptized or having attended any church or ever having been a member or identified with a church.
Sure, and every fat, loud mouthed drunk who claims to have been a Navy SEAL or Army Green Beret can legitimately self identify too and some dufus would accept it if he were trying to deceitfully prove a point......
It's true! I just answered a telephone survey tonight and one of the questions was to identify "religious" leanings. The options were: Christian, Jewish, Muslim, no religious leanings or Other. When I answered, Christian, I was asked to identify what kind of Christian: Catholic, Protestant, Mormon or Other.
It is often the same thing here with the few Catholic bigots that attempt to categorize everyone who isn't a Catholic and who can barely stand to consider us as fellow Christians. The catch-all is "Protestant" even though many of us do NOT identify with the mainline Protestant denominations and actually prefer to be known as Christians, alone. We understand that the sign outside the church door does not define us but only that Gospel which is found in Holy Scripture and we know our true Shepherd, the Lord Jesus Christ.
Perhaps the real problem with Democrat-voting Catholics or other Christians, who not only vote for those opposed to their church's stated beliefs but who function as non-Christians every day of the week but Sunday, is they do not know the true Shepherd in their hearts but have a facade of religiosity and no desire for anything deeper. Those who know the Savior are indwelt with His Spirit and there is an internal urging that enables us to recognize what is right and true and good. This can be ignored, of course, but it IS there and there is no excuse.