I've posted (or at least thought about posting; I can't be bothered to actually find the post) about a welcome mat with the words "Come back with a warrant" on it. As someone who values my own rights and privacy, that would be my natural and instinctive response to a police officer making inquiries about a search of my home -- because consenting to a search when you are under suspicion is never a good idea.
That's why I'm a Libertarian, not a Republican. Asserting one's constitutional rights should never be grounds for suspicion. If the government didn't have probable cause for a search before being denied permission, the fact that it was denied doesn't give any additional evidentiary weight in favor of a warrant.
To disregard this is to render Constitutional rights meaningless. If any refusal can be considered evidence for a compulsory search, then there is no right to refuse a search.