"[Re: Implementation of the State's "police powers"] "....The mode or manner in which those results are to be accomplished is within the discretion of the state, subject, of course, so far as Federal power is concerned, only to the condition that no rule prescribed by a state, nor any regulation adopted by a local governmental agency acting under the sanction of state legislation, shall contravene the Constitution of the United States, nor infringe any right granted or secured by that instrument. A local enactment or regulation, even if based on the acknowledged police powers of a state, must always yield in case of conflict with the exercise by the general government of any power it possesses under the Constitution, or with any right which that instrument gives or secures. Gibbons v. Ogden, 9 Wheat. 1, 210, 6 L. ed. 23, 73; Sinnot v. Davenport, 22 How. 227, 243, 16 L. ed. 243, 247; Missouri, K. & T. R. Co. v. Haber, 169 U.S. 613, 626, 42 S. L. ed. 878, 882, 18 Sup. Ct. Rep. 488."

'The question of constitutional law to which we have referred [the equal protection of the laws] cannot be disposed of by saying that the statute in question may be referred to what are called the police powers of the state, which, as often stated by this court, were not included in the grants of power to the general government, and therefore were reserved to the states when the Constitution was ordained. But, as the Constitution of the United States is the supreme law of the land, anything in the Constitution or statutes of the states to the contrary notwithstanding, a statute of a state, even when avowedly enacted in the exercise of its police powers, must yield to that law. No right granted or secured by the Constitution of the United States can be impaired or destroyed by a state enactment, whatever may be the source from which the power to pass such enactment may have been derived. 'The nullity of any act inconsistent with the Constitution is produced by the declaration that the Constitution is the supreme law.' The state has undoubtedly the power, by appropriate legislation, to protect the public morals, the public health, and the public safety; but if, by their necessary operation, its regulations looking to either of those ends amount to a denial to persons within its jurisdiction of the equal protection of the laws, they must be deemed unconstitutional and void. Gibbons v. Ogden,, 9 Wheat. 1, 210, 6 L. ed. 23, 73; Sinnot v. Davenport,, 22 How. 227, 243, 16 L. ed. 243, 247; Missouri, K. & T. R. Co. v. Haber, 169 U.S. 613, 626, 42 S. L. ed. 878, 882, 18 Sup. Ct. Rep. 488.'

"[S]tate law can be pre-empted in either of two general ways. If Congress evidences an intent to occupy a given field, any state law falling within that field is pre-empted. [Pacific Gas & Electric Co. v. State Energy Resources Conservation & Development Comm'n, 461 U.S. 190,] 203-204 [(1983)]; Fidelity Federal Savings & Loan Assn. v. De la Cuesta, 458 U.S. 141, 153 (1982); Rice v. Santa Fe Elevator Corp., 331 U.S. 218, 230 (1947). If Congress has not entirely displaced state regulation over the matter in question, state law is still pre-empted to the extent it actually conflicts with federal law, that is, when it is impossible to comply with both state and federal law, Florida Lime & Avocado Growers, Inc. v. Paul, 373 U.S. 132, 142-143 (1963), or where the state law stands as an obstacle to the accomplishment of the full purposes and objectives of Congress, Hines v. Davidowitz, 312 U.S. 52, 67 (1941)." Silkwood v. Kerr-McGee Corp., supra, at 248."

..." As we explained in Hillsborough County v. Automated Medical Laboratories, Inc., 471 U.S. 707, 718 (1985), it is appropriate to expect an administrative regulation to declare any intention to pre-empt state law with some specificity:

"[B]ecause agencies normally address problems in a detailed manner and can speak through a variety of means, . . . we can expect that they will make their intentions clear if they intend for their regulations to be exclusive. Thus, if an agency does not speak to the question of pre-emption, we will pause before saying that the mere volume and complexity of its regulations indicate that the agency did in fact intend to pre-empt."

...."These problems are avoided, of course, if the calculatedly vague consequences the passage recites— 'incorporated into the operations of the national government' and 'rendered auxiliary to the enforcement of its laws'—are taken to refer to nothing more (or less) than the duty owed to the National Government, on the part of all state officials, to enact, enforce, and interpret state law in such fashion as not to obstruct the operation of federal law, and the attendant reality that all state actions constituting such obstruction, even legislative acts, are ipso facto invalid. See Silkwood v. Kerr-McGee Corp., 464 U. S. 238, 248 (1984) (federal pre-emption of conflicting state law). This meaning accords well with the context of the passage, which seeks to explain why the new system of federal law directed to individual citizens, unlike the old one of federal law directed to the States, will 'bid much fairer to avoid the necessity of using force' against the States...."