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If you look at congress, these are all about us-congress, and the latter tag is bigger. So perhaps a merge from congress->us-congress is in order? I don't think a synonym is necessary, or desirable, since there can be non-US Congresses.
I've made congress the master tag.
I think locale tags would do a much better job of distinguishing questions for non US congresses. For example, I think guatemalacongress is a bit more useful than guatemala-congress.