WASHINGTON (CNN) -- Former Vice President Al Gore called on Congress and the public to resist what he called "a gross and excessive power grab" by the Bush administration amid the war on terrorism, declaring that "our Constitution is at risk."
Gore said the use of the National Security Agency to eavesdrop on Americans without a court order shows that President Bush "has been breaking the law repeatedly and persistently."
"A president who breaks the law is a threat to the very structure of our government," he said.
Gore, Bush's Democratic opponent in the bitter 2000 election, spoke to the Liberty Coalition, which calls itself a "transpartisan" group concerned with civil liberty and privacy issues.
Bush has defended his use of the NSA to intercept international communications of people in the United States suspected of having links to terrorist groups, telling reporters the program is legal and necessary to fight terrorism. The president and other top officials argue that Congress gave him the power to act without the approval of a special panel of judges established by Congress under the Foreign Intelligence Surveillance Act of 1978.
Sen. Arlen Specter, chairman of the Senate Judiciary Committee, has disputed that assertion.
Gore said lawmakers specifically refused to give Bush that power when they authorized the use of force after the September 11, 2001, attacks.
Gore said the wiretaps -- combined with Bush's assertion of the power to hold American citizens indefinitely as "enemy combatants," the authorization of harsh treatment of prisoners and his use of signing statements to declare how he will interpret a law passed by Congress -- have "brought our republic to the brink of a dangerous breach in the fabric of the Constitution."
"The disrespect embodied in these apparent mass violations of the law is part of a larger pattern of seeming indifference to the Constitution that is deeply troubling to millions of Americans in both political parties," he said.
Gore said the dangers of unchecked executive power can be seen in the war in Iraq, which the administration warned was necessary because Iraq was concealing chemical and biological weapons and trying to produce nuclear arms. No such weapons were found after the March 2003 invasion.
He quoted "1984" author George Orwell, who wrote that people are capable of believing things that aren't true until "a false belief bumps up against solid reality, usually on a battlefield."
"Twenty-two hundred American soldiers have lost their lives as this false belief, as this belief bumped into a solid reality," he said. "And indeed, whenever power is unchecked and unaccountable, it almost inevitably leads to gross mistakes and abuses."
To emphasize the bipartisan nature of Monday's event, organizers had planned to have former U.S. Rep. Bob Barr of Georgia -- one of the House managers during President Clinton's 1999 impeachment trial -- introduce Gore via videolink. But technical problems prevented Barr, a conservative critic of the NSA program and a frequent CNN contributor, from speaking.
"In spite of our differences over ideology and politics, we are in strong agreement that the American values we hold most dear have been placed at serious risk by the unprecedented claims of the administration to a truly breathtaking expansion of executive power," Gore said.
Gore said the Republican leadership of Congress has acted "as if it is entirely subservient to the executive branch," with lawmakers too busy raising money for re-election to challenge Bush.
"Though I sympathize with the awkward position in which these men and women were placed, I cannot disagree with the Liberty Coalition when it says that Democrats as well as Republicans in the Congress must share the blame for not taking action to protest and seek to prevent what they consider a grossly unconstitutional program," he said.
He also called on Attorney General Alberto Gonzales to appoint a special prosecutor to investigate the warrantless wiretapping program -- and he urged voters to make it an issue in November's congressional races, because "our Constitution is at risk."