Final answer:
Members of Congress can overturn a president's unilateral action through veto overrides, limiting the president's power, and the impeachment process.
Step-by-step explanation:
Members of Congress can overturn a president's unilateral action through various means other than legislation. One way is through the use of veto overrides. If the president vetoes a bill, Congress can override the veto with a two-thirds majority vote in both the House and the Senate, making the bill law despite the president's objections.
Another way Congress can check a president's unilateral action is by limiting the president's power. For example, Congress can refuse to declare war or provide funds for the military, preventing the president from taking unilateral actions in the context of national security.
Additionally, Congress has the authority to check the president's power through the impeachment process. If the president is found guilty after being impeached by the House of Representatives, the Senate can remove the president from office.