C. The Taxing and spending power
The Taxing and spending power of Congress is stated in Article I, Section 8, Clause 1 of the United States Constitution:
The Congress shall have Power To lay and collect Taxes, Duties, Imposts (form of tax) 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
The Congress' power to manage the domestic and foreign debts as well as the budget necessary for the funding of the military defense gives the Congress the right to check for powers of the president, concerning foreign affairs since the President would have to adjust its decision in the foreign area to the nation's budget which is based on the income from taxes lay and collected by Congress.