Recently some critics of prominent Trump-supporting Dallas Baptist pastor Robert Jeffress have disapprovingly identified him as a supporter of “Two Kingdoms” theology, an historic Protestant belief about the division of duties between spiritual & earthly rule. Jeffress in public pronouncements has stressed that civil government is called to provide public order, not embody the Sermon on the Mount, on issues like immigration.
Two kingdoms theology’s most expansive expression is Augustine’s City of God, written late in the game for another world power, the Roman Empire (well, the western part.) In those times those in civil authority who “wore the belt” were not allowed to become priests. The system was so corrupt at that stage that Christianity could not see its way clear to fix it (although it made improvements such as getting slavery to dissipate.) Rome collapsed, but the Church, in a different way, laid the foundation for a civilisation that was greater than the one that was there.
I honestly don’t think that the howling social justice warriors who profess and call themselves Christians (and I’ve run into them of late) have really thought through what the New Testament commands us to do vs. what the state should do. The blunt truth is that, like it or not, Christianity has never really set forth a morality for the state, or that the morality of the state should be at unity with that in the church. The religion that has done that is Islam; that may explain in part the affinity that people on the left feel with Islam. Even a secular historian like Ferdinand Lot grasped that truth. Since most of the focus on refugees have been those from the Middle East, it pays to look and see how things have worked out under the various forms of Islam before we unwittingly advocate those things for ourselves.