Several congressional Republicans said Sunday that they would be open to increasing the amount of money the government collects in taxes, with a senior Republican member of the U.S. Senate going so far as to say he is willing to break his earlier promise to not support tax hikes in any form.

Sen. Lindsey Graham (R-S.C.) said he opposes raising income tax rates, but that he is open to increasing tax revenue by reducing the availability of deductions for things like charitable giving and mortgage interest. Sen. John McCain (R-Ariz.) also said Sunday that he would support limiting deductions.

Doing so would violate Grover Norquist's "Taxpayer Protection Pledge," which both men have signed (as have most Republicans in Congress). Under the pledge, "candidates and incumbents solemnly bind themselves to oppose any and all tax increases," according to the Americans for Tax Reform site.

"When you're $16 trillion in debt, the only pledge we should be making to each other is to avoid becoming Greece, and Republicans -- Republicans should put revenue on the table," Graham said on ABC's "This Week with George Stephanopoulos." "