U.S. Constitution Article I Section 8
"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;"
Seems like welfare and defense is in the Constitution.
It certainly doesn't mean Welfare in the direct way in which it's being referred to in this thread...
The United States Constitution contains two references to "the General Welfare", one occurring in the Preamble and the other in the Taxing and Spending Clause. The U.S. Supreme Court has held the mention of the clause in the Preamble to the U.S. Constitution "has never been regarded as the source of any substantive power conferred on the Government of the United States or on any of its Departments."
Read this...
http://constitutionmythbuster.com/2011/05/09/what-does-the-general-welfare-clause-really-mean/