The task of answering that question is the job of the Supreme Court.
In order to have them think about the question and produce an official answer,
somebody has to bring the case to the Court, and claim that Congress doesn't
have that right. Without a case being filed, the Supreme Court doesn't do anything
with the question, and the answer remains a matter of opinion and conjecture to most, while to others it constitutes a clear example of fascist power-grab.
Added: The matter was never tested in court - the Feds "persuaded" the states to lower the speed limit with the not-so-veiled threat of withholding their federal highway funds.
The Constitution vested Congress with the authority to regulate trade with other nations, between the states, and with Native American Tribes in the Interstate Commerce Clause (Article I, Section 8, Clause 3).
The policies of the president and Congress affect the relationship between federal and state government.
congress
Congress
congress generally must approve interstate compacts, they involve several states.
First: Congress may regulate the use of the channels of interstate commerceSecond: Congress is empowered to regulate and protect the instrumentalities of interstate commerce, or persons or things in interstate commerce, even though the threat may come only from intrastate activitiesThird: Congress' commerce authority includes the power to regulate those activities having a substantial relation to interstate commerce... i. e., those activities that substantially affect interstate commerce
congress generally must approve interstate compacts, they involve several states.
Regulate interstate trade.
the interstate commerce commission
the commmerce power- the power of congress
Congress could not regulate foreign and interstate commerce.
Article I, Section 8 of the Constitution assigns that authority to Congress in the "Interstate Commerce Clause."