McCain, appearing on the "Fox News Sunday" television program, showed no sign he was ready to back away from his proposal outlawing torture that has drawn bipartisan support.
Asked how far he was willing to push the issue over the objections of the White House, McCain, who belongs to Bush's Republican party, said: "As far as necessary."
McCain said the measure enjoys widespread support among US voters and former senior national security officials and retired military officers, including former career soldier and diplomat Colin Powell who served as Secretary of State during Bush's first term.
"We had a vote in the Senate of 90 to nine. (An) overwhelming majority of the American people do not approve of this kind of exemption. People ranging from Colin Powell to literally every national security advisor or chairman of the Joint Chiefs have said that we can't do this kind of thing," McCain said.
The Senate last week reaffirmed its support for McCain's amendment after having voted 90-9 a month ago to "prohibit cruel, inhuman and degrading treatment of persons in the detention of the US government," according to the text of the measure.
To become law, the lower legislative chamber, the House of Representatives, would have to approve it and the president would have to sign it.