According to this quote, how should the issue of slavery in a territory be decided? By the residents of a territory
By the US Supreme Court
By the US Congress
By the President

By the residents of a territory.

Explanation:

Note the quote, quote:

"In my opinion, the people of a Territory can, by lawful means, exclude slavery from their limits prior to the formation of the State Constitution... [regardless of] what way the Supreme Court may hereafter decide..."

As duly stated in the quote from the excerpt given to you, the author wants the people of the territory (or state in any case) to decide on their own whether or not they want to be a slave state or not.

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