Under the Tenth Amendment and the structure of the Constitution, if a power is not delegated to the federal government in the Constitution, that power is reserved to the states respectively.  Since nullification and interposition are not delegated to the federal government, nor are the states prohibited from doing so, the states retain the power of nullification and interposition.

Additionally, Article VI of the U.S. Constitution requires every government official at all levels in all branches of the government to "support this Constitution."  Article 16, Section 1 of the Texas Constitution codifies that oath in Texas to say that every government officer whether elected or appointed shall swear to "preserve, protect, and defend" the U.S. Constitution and the Texas Constitution.

If you are sworn to protect the Constitution, and you see it being violated, you are duty bound to use the powers of your office to stop the violation.