THE POWER TO SIGN TREATIES is not a concurrent power.
In politics, concurrent power refers to the power that is shared by both the federal government and the state government. This type of power can be exercised by both level of government simultaneously among the people of the country. In the United States of America, examples of concurrent powers are: establishing a court system, levying tax, election regulation, borrowing funds, etc. The signing of treaties and conduction of foreign policies is a power given to the federal government only; the state governments do not have the power to sign treaties
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When they what? Please provide a full question!