The problem is that many Christians who are Democrats see welfare is using the state to perform charity, help the poor, help the sick, etc.
Then supporting the big government is seen as a Christian obligation, while lessening the demand on the church and on them personally except writing a tax check.
Aside from that statement I underlined being oxymoronic, the welfare state is not a part of Christianity at all. The Bible warns against establishing big government because it promotes slavery and disease instead of health and freedom (1 Samuel 8:10-18).
many Christians who are Democrats see welfare is using the state to perform charity, help the poor, help the sick, etc.