Here's why:
* It's a proper noun: The "Commerce Clause" is a unique and specific part of the Constitution, like the "First Amendment" or the "Bill of Rights." Proper nouns are capitalized.
* It's a legal term: The Commerce Clause has specific legal implications and is commonly used in legal discussions and documents.
Example:
"The Commerce Clause of the Constitution grants Congress the power to regulate interstate commerce."
However, if you're referring to the concept of commerce in general, you wouldn't capitalize it.
Example:
"The rise of electronic commerce has transformed the global economy."