Because in 1798, Jefferson had co-authored a resolution for the legislatures of Virginia and Kentucky that affirmed the states' right to resist federal encroachments on their powers. Through the principle of "nullification" that would later be codified into the Tenth Amendment, the States could locally override unconstitutional federal laws.

"When all government, domestic and foreign, in little as in great things, shall be drawn to Washington as the center of all power, it will render powerless the checks provided of one government on another, and will become as venal and oppressive as the government from which we separated" ~ Thomas Jefferson. But ten years later, the General Government was struggling with more practical problems such as the quasi-war on the high seas with the British in league with America's former allies, the French. Now in the White House, expediency required Jefferson to compromise his own principles. He imposed an embargo under which no American ship could depart for any foreign port anywhere in the world, hoping that this economic warfare would hurt British and French prosperity, forcing their governments to change tack.

But the decision would have dire consequences for the trading economies on the eastern seaboard. In the landmark case of "United States v. The William", the embargo was ruled unjust, unconstitutional and oppressive.

"While this State [of Massachusetts] maintains its sovereignty and independence, all the citizens can find protection against outrage and injustice in the strong arm of the State government," they said. The embargo, furthermore, was "not legally binding on the citizens of this State".

 

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