In the US, those who hold federal office take an oath to uphold the Constitution. There is unquestionable precedence that the Constitution limits laws made on religious grounds. Though, this Constitutional limit has not been consistently applied historically (in God we trust is on our money, for example). If someone makes this oath of office, and shares your opinion that they cannot create or approve a law that goes against their biblical interpretation, then they have created a bit of a problem for themselves by taking this oath. Your biblical interpretation limits their ability to follow through on their oath of office. And it’s hard not to see them taking the oath, while holding the scriptural belief, as a form of deceit. Since there is scripture that prohibits deceit, it’s hard to see a solution to this except a) not accept office or b) adjust one of the interpretations. Not sure of a good Constitutional solution for them, since a unilateral forging of new precedent is practically impossible. Perhaps these Christian lawmakers have a different understanding of spreading the Gospel. Maybe even different thoughts about the relationship between following God’s law and federal law.