Dormant Commerce Clause vs. Privileges and Immunities Clause (Article IV)

"I remain unclear on the best and simplest approach to Commerce Clause vs. Principles and Immunities Clause of Art. IV. - not sure about the distinctions or when to apply which."

Response:

Both concepts deal with state laws, which make these two concepts confusing. First look to see whether the state law discriminates against out-of-state residents. If it does not, then do not apply the Privileges and Immunities ("P&I") clause. If it does, then you'll need to distinguish between P&I, and Dormant Commerce clause ("DCC")

If the state law discriminates, then it will fail under the P&I clause if the law prevents out-of-state residents from achieving their livelihood in the state, (ie, important economic interests), or, if the law prevents them from having their civil liberties. The only way such a law will not fail is if the state can prove that there is a substantial justification for the law, and that there are no less restrictive means.

If the state law discriminates, then it will also fail under DCC, if the law burdens interstate commerce. The only way the law will not fail is if it furthers an important non-economic state interest, and there are no reasonable nondiscriminatory alternatives, or if the state is acting as a market participant (often tested on the MBE), or if the law involves action regarding performance of a traditional government function.

You should note that unlike with P&I clause, a state law can violate DCC, even if it is non-discriminatory. But, if the law is non-discriminatory (and burdens interstate commerce), then the law will fail only if the burden outweighs the state interest in passing the law.

My advice, should you come to a question requiring an analysis of these concepts, is to first determine if the law is discriminatory. If not, then, if the law burdens interstate commerce, apply DCC only. If it is discriminatory, and burdens interstate commerce, then apply both DCC, and P&I, using the analysis above.