Former US presidential candidate George McGovern says the case for impeaching President Bush is "far stronger" than it was against Richard Nixon.
Mr McGovern lost the 1972 presidential election to Nixon, who resigned in 1974 amid the Watergate scandal.
George W Bush is guilty of "numerous impeachable offences", Mr McGovern writes in a Washington Post article.
These include, he says, the Iraq war, the Guantanamo detentions and the neglect of Hurricane Katrina's victims.
"As we enter the eighth year of the Bush-Cheney administration, I have belatedly and painfully concluded that the only honourable course for me is to urge the impeachment of the president and the vice-president," reads the start of Mr McGovern's article.
He stood clear of calls to impeach Nixon, Mr McGovern writes, fearing that it would be seen as an expression of personal vengeance towards the man who had beaten him in the 1972 election.
But now, Mr McGovern says, his choice is different.
President Bush and Vice-President Cheney "have repeatedly violated the Constitution. They have transgressed national and international law. They have lied to the American people time after time".
The case against them is far stronger than the case against Nixon and Vice-President Spiro Agnew, he writes.
Mr McGovern lists a series of events and issues to support his call for impeachment.
As well as the "murderous, illegal, nonsensical war against Iraq", Mr McGovern cites the shipping of prisoners from Afghanistan to Guantanamo Bay and other countries for interrogation in violation of habeas corpus.
Mr McGovern also mentions what he terms the "scandalous neglect and mishandling" of the Hurricane Katrina catastrophe.
He also quotes Elizabeth Holtzman, who played a key role in the Nixon impeachment proceedings and has herself called for Mr Bush's impeachment.
Two years ago, Ms Holtzman wrote: "It wasn't until the most recent revelations that President Bush directed the wiretapping of hundreds, possibly thousands, of Americans, in violation of the Foreign Intelligence Surveillance Act (FISA) - and argued that, as Commander in Chief, he had the right in the interests of national security to override our country's laws - that I felt the same sinking feeling in my stomach as I did during Watergate."
Impeachment is unlikely, Mr McGovern says, but Congress must still be urged to act.
It would be a way to "signal to the American people and the world that some of us feel strongly enough about the present drift of our country to support the impeachment of the false prophets who have led us astray".
Mr McGovern, who ran on a platform advocating withdrawal from Vietnam, lost the 1972 election to incumbent Richard Nixon by a landslide.
During the election campaign there was a break-in at the offices of the Democratic Party's national headquarters in the Watergate complex in Washington DC.
Five men connected with Nixon's campaign team were arrested and evidence of a cover-up gradually emerged, implicating Nixon himself.
The House Judiciary Committee recommended his impeachment in July 1974.
He was accused of obstructing justice, abusing presidential powers and withholding evidence from the courts.
Faced with certain removal from office, Nixon announced his resignation in August that year.