The most likely answer is that this data would be nominal. Depending on how the political scientist was gathering the data, it could conceivably be ordinal or even interval. But this is much less likely than nominal.
If the researcher were trying to study the political ideology of the church members, the data might be ordinal or even interval. The researcher could try to create a scale (which would be very difficult to construct well) of how liberal or conservative the church members are. That data would be ordinal or interval.
However, if the research is only on political affiliation (are you a Democrat, Republican, Independent or Other), the data would be nominal. Nominal data are data that simply get put into different categories with different names (therefore the designation of “nominal”). These data cannot be given number values that make one greater than the other as in ordinal or interval data.