“Cannabis: The reason it's not in the Constitution is because letting states and individuals decide is in the Constitution. That thing of beauty is called the Tenth Amendment: "The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.”

2000s, The Real Abraham Lincoln: A Debate (2002), Rebuttal

AP report with lead summarizing of remarks stating "Robert F. Kennedy said yesterday that the United States — despite Alabama violence — is moving so fast in race relations a Negro could be President in 40 years." "Negro President in 40 Years?" in Montreal Gazette (27 May 1961) http://news.google.com/newspapers?nid=1946&dat=19610527&id=y40tAAAAIBAJ&sjid=F50FAAAAIBAJ&pg=5424,5208719
Context: The Irish were not wanted there [when his grandfather came to Boston]. Now an Irish Catholic is president of the United States … There is no question about it. In the next 40 years a Negro can achieve the same position that my brother has. … We have tried to make progress and we are making progress … we are not going to accept the status quo. … The United States Government has taken steps to make sure that the constitution of the United States applies to all individuals.

Opinion on the Constitutionality of the Bill for Establishing a National Bank., 1791. http://www.yamaguchy.netfirms.com/7897401/jefferson/natbank.html ME 3:146
Posthumous publications, On financial matters

1830s, Illinois House Journal (1837)

Speech before Congress (3 December 1860).
Context: The course of events is so rapidly hastening forward that the emergency may soon arise when you may be called upon to decide the momentous question whether you possess the power by force of arms to compel a State to remain in the Union. I should feel myself recreant to my duty were I not to express an opinion on this important subject.
The question fairly stated is, Has the Constitution delegated to Congress the power to coerce a State into submission which is attempting to withdraw or has actually withdrawn from the Confederacy? If answered in the affirmative, it must be on the principle that the power has been conferred upon Congress to declare and to make war against a State. After much serious reflection I have arrived at the conclusion that no such power has been delegated to Congress or to any other department of the Federal Government. It is manifest upon an inspection of the Constitution that this is not among the specific and enumerated powers granted to Congress, and it is equally apparent that its exercise is not "necessary and proper for carrying into execution" any one of these powers. So far from this power having been delegated to Congress, it was expressly refused by the Convention which framed the Constitution.

1850s, The House Divided speech (1858)

Letter to Justice William Johnson (1823)
1820s

Striking down the "Take-Title" provision of the Low-Level Radioactive Waste Policy Amendments Act in New York v. United States, 505 U.S. 144 (1992).

On the Irrepressible Conflict (1858)
Context: The Union is a confederation of States. But in another aspect the United States constitute only one nation. Increase of population, which is filling the States out to their very borders, together with a new and extended network of railroads and other avenues, and an internal commerce which daily becomes more intimate, is rapidly bringing the States into a higher and more perfect social unity or consolidation. Thus, these antagonistic systems are continually coming into closer contact, and collision results.
Shall I tell you what this collision means? They who think that it is accidental, unnecessary, the work of interested or fanatical agitators, and therefore ephemeral, mistake the case altogether. It is an irrepressible conflict between opposing and enduring forces, and it means that the United States must and will, sooner or later, become either entirely a slaveholding nation, or entirely a free-labor nation.