"Flatters, panders, coasting, front-runner, looking for a coronation. ... She has no political fortitude," Nader said of Clinton during a radio appearance when he was asked to describe the former First Lady.
"She's just another bad version of (former President) Bill Clinton," he told KGO radio.
Nader, whose Green Party candidacy for president in 2000 was blamed for helping put George Bush in the White House by siphoning votes from Vice President Al Gore, said he was considering running again in 2008.
"We're going to see what the Democrats come up with," he said.
Nader, who was in San Francisco promoting a new memoir, "The Seventeen Traditions," also has been hard on other Congressional Democrats during his book tour, including House Speaker Nancy Pelosi, a San Franciscan.
He said he planned to visit Pelosi's office in the city to protest the war in Iraq.
While Nader received 2.7 percent of the vote in 2000, he got less than one-half of 1 percent in 2004.
Phil Trounstine, who heads the San Jose State Center for Policy and Research, said Nader's flirtation with another presidential bid is viewed by many as evidence that he is on "an enormous ego trip with potentially destructive impact."