How can a bill become law if the governor vetoes it?

Remember, Congress has two parts: the House of Representatives and the Senate. Each has an equal role in making laws at the federal level. A bill can begin in either the House or the Senate, but in the end both must agree to an identical bill and gain the president's approval before it can become law.

Several committees are part of the lawmaking process. Remember, when members of the House and Senate come together to compromise on a bill, this is called a conference committee.

Explanation:

In easier terms, Congress needs 2/3 vote to override the veto, this helps keep  equal power amoug the branchs.

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