
Quoting
Litigator
Yes, the officer can do this because what he sees in public does not constitute a search. For example, if he ran your tags and they came back expired, he could pull you over for that. It sounds like that is what happened--the violation would be driving a car with expired tags--there need be no further or additional violation to justify pulling you over. If thereafter he smelled alcohol, etc., that would lead to probable cause to arrest for DWI.
You might want to clarify what it means that you were pulled over for a warrant--how do you know this and what exactly was said? Or were you in fact pulled over for expired tags?