How did a 55 mph speed limit get established in many states, when it was an initiative in the Federal government? And, where was the authority in the Constitution to have the Federal government change those speed limits in the respective states?
Same thing goes for the raising of the drinking age from 18 to 21 in the mid-1980s
Why are the Legislature, Executive, and Judicial branches of government in DC referred to as 'Federal', rather than 'National'?
For what purpose was the Constitutional Convention called?
If the States are only administrative branches of the government in DC, why do they have their own legislatures, executives, and judiciary?
For what purpose, prior to the 16th Amendment, were Senators to DC appointed by State legislatures, rather than popular elections in their respective states?
Why is there an electoral college?
What is the 'incorporation' clause of the 14th amendment, and why was it deemed necessary? These are some of the questions off the top of my head. I have some more for later, if you'll bear with me.
My bad. 16th Amendment should read 17th amendment.
Speed limits were and are somewhat varied throughout the states. This was true 40 years ago and is true today. Uniformity has been forced through the blunt instrument of highway funds but has never really been that consistent. There is full constitutional authority to establish speed limits on US highways as well as Interstates. State and country roads are not affected.
Drinking age legislation has been justified through the Commerce clause and I don't have much argument with that since liquor is part of interstate commerce and has had federal connections for centuries. Its sale and impact does not stop at state borders.
It is a distinction without a difference since Madison described the government as partly federal and partly National. But the Constitution was to establish a Union which is national though created through federalism. Our Founders did not want a monolithic National government which overroad all state and local power thus power to regulate at those levels was left primarily with state legislatures.
The CC was called to reduce the power of state governments and increase that of the federal government. This produced the anti-Federalist opposition which did not agree with the aim and fought the ratification.
State governments are not arms of the federal government though Madison wanted to make them just that prior to the CC. Local concerns were left to local institutions such as legislatures, courts, executive but they differed greatly in their natures and powers.
Senators were to represent the permanent National Interest and be above politics to some degree. The Senate was to be analogous to the House of Lords outside democratic control. Given the degree of corruption and cupidity within the typical state legislatures I see no current benefit to the original method of selection but would not oppose returning to the old method. Illinois would likely be represented by the same party hacks who typically represent it in the Senate a disgusting lot at best.
Executive election was not left in the hands of the people at large because of distrust of democracy. Legislatures were to appoint in any manner they chose electors who would vote for President. They could use an election, a lottery, a dart board whatever. It was felt that screening that choice from direct popular influence was the best procedure. It should be recalled that during that era Democracy was a negative term synonymous with mobocracy.
I am not familiar with the term "incorporation clause" wrt the 14th. But as to the need for the amendment as a whole it was to prevent the Slavers from re-enslaving the slaves in fact if not in name through the suppression of their rights and political power.