quote:
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In the early 1980s the Social Security program faced a serious short-term financing crisis. President Reagan appointed a blue-ribbon panel, known as the Greenspan Commission, to study the financing issues and make recommendations for legislative changes. The final bill, signed into law in 1983, made numerous changes in the Social Security and Medicare programs, including the taxation of Social Security benefits, the first coverage of Federal employees under Social Security and an increase in the retirement age in the next century. (Summary of the provisions of the '83 Amendments)
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second and third quote:
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Section. 7.
Clause 1: All Bills for raising Revenue shall originate in the House of Representatives; but the Senate may propose or concur with Amendments as on other Bills.
Section. 8.
Clause 1: The Congress shall have Power To lay and collect Taxes, Duties, Imposts and Excises, to pay the Debts and provide for the common Defence and general Welfare of the United States; but all Duties, Imposts and Excises shall be uniform throughout the United States;
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As defined by the US Constitution, the Congress writes the tax laws so Congress is responsible for them in whatever form the laws exist, as a majority of the congress voted for the laws.
The executive can sign the law but cannot effectively veto if the support in congress is strong enough (2/3).