President Bush's decision to use the secretive National Security Agency to monitor some domestic communications as part of the war on terror remains the focus of intense debate in Congress and among legal scholars.
The Bush administration says the NSA program targets international calls either to or from the United States that involve people with suspected links to terrorism.
The eavesdropping effort bypasses a 1978 law that requires the government to get a warrant from a special surveillance court before phone calls and other communications involving U.S. citizens or legal residents can be monitored.
Opposition Democrats have taken the lead in questioning the legality of the domestic spying effort, which they say is a threat to civil liberties.
"I believe they are running roughshod over the Constitution and are hiding behind inflammatory rhetoric, demanding Americans blindly trust their decisions," said Patrick Leahy of Vermont, the top Democrat on the Senate Judiciary Committee.
Bush administration officials contend that the president has the power to authorize the program under the general authority granted to him in the Constitution to protect the country during wartime and because Congress authorized military action against Afghanistan in the wake of the 2001 terrorist attacks.
But even some conservative legal scholars are raising objections to what they see as an overly broad interpretation of presidential power.
"The theory invoked by the president to justify eavesdropping by the NSA in contradiction to FISA [Foreign Intelligence Surveillance Act] would equally justify mail openings, burglaries, torture or internment camps, all in the name of gathering foreign intelligence," said Bruce Fein, a legal expert who worked in the Justice Department during the Reagan administration. "Unless rebuked, it will lie around like a loaded weapon, ready to be used by any incumbent who claims an urgent need." He testified at a recent Senate hearing on the domestic surveillance program.
Supporters of the domestic spying program counter that the effort is narrowly targeted and is a necessary tool in the war on terror.
James Woolsey served as the director of the Central Intelligence Agency for a time during the Clinton administration. He told the Senate Judiciary Committee that the 1978 law, known as FISA, or the Foreign Intelligence Surveillance Act, is outdated.
"We are in the gun sights of more than one international terrorist Islamist organization that have ties, some of them, to states. And these are shifting alliances," he said. "This is a hard kind of thing to keep up with and trying to do it spy by spy, case by case, pleading by pleading, as one does in the FISA [Foreign Intelligence Surveillance Act] court, is not only difficult, it is absolutely impossible."
The White House has been focused in recent weeks on reassuring conservatives as well as liberals that the NSA monitoring program targets only those with suspected links to terrorists and does not threaten civil liberties.
"It is focused solely on international communications that involve a known al-Qaida or suspected al-Qaida terrorist or affiliated al-Qaida terrorist," said presidential spokesman Scott McClellan.
Congressional Republicans are now struggling to find a unified proposal that would allow the legislative branch to have oversight on the surveillance program.
But many legal experts believe the issue will eventually wind up before the Supreme Court, which may have to decide whether the president overstepped his authority by ignoring a law enacted by Congress. University of Virginia political analyst Larry Sabato says the debate is not a new one.
"This is an enduring controversy. We are going to see the same arguments made in 2006 that have been made repeatedly in American history. I doubt we come any closer to resolving the ultimate dispute. You have top reach some kind of reasonable balance between individual liberty and security," he said.
Professor Sabato also says the eavesdropping controversy could be an issue in the November congressional election campaign.