What is the most effective way for congress to prevent a presidents foreign policy

to cut off budget support for that policy.

Explanation:

The most effective way for congress to prevent a president's foreign policy is to cut off budget support for that policy. If the budget support for the policy is cut, then the president cannot carry out his plans due to a lack of resources. In this way, the powers of the president are limited due to the authority of Congress, in a system that is called checks and balances.

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