In a letter to Bush, Democrat Boxer said she had never seen such widespread opposition among her constituents to a Cabinet nominee.
Boxer said one of her major concerns is the way Ashcroft blocked the appointment of African-American Judge Ronnie White to the federal bench.
"I hate to use a charged term, but it's my heart talking here," she told Schieffer. "I really think it was a political lynching that happened in the United States Senate."
Asked whether she thinks Ashcroft is a racist, Boxer replied: "I never use that word against anyone. I can only judge John Ashcroft by his actions and what I am telling you is that he engineered a humiliating defeat for Ronnie White."
White will testify next week at Ashcroft's confirmation hearing a session that may be even more bruising than expected.
Two other Democratic senators, meanwhile, toned down their early support for the attorney-general nominee. Sen. Bob Torricelli of New Jersey said Wednesday he would vote to confirm Ashcroft only if he promises to keep the Justice Department involved in monitoring racial profiling by New Jersey state troopers.
Supporters of John Ashcroft are angry that foes of his nomination as attorney general have access to boxes of opposition research done by the late Gov. Mel Carnahan's campaign.
Ashcroft wasn't talking as he scurried through the Capitol trying to round up support, but Boxer's opposition came just 24 hours after more than 200 groups representing everything from civil rights to consumer advocates said they'll work together to kill his nomination.
Also Wednesday, in an effort to show that Ashcroft's views are not mainstream, opponents circulated an old Ashcroft Christmas Card in which he listed a visit to Bob Jones University, the school that once banned interracial dating, as one of his highlights of 1999.
The Rev. Jesse Jackson, leading the anti-Ashcroft charge, has said civil rights groups and organized labor will join together to confront Democrats at public events in their home states, demanding "no" votes on Ashcroft.
Black leaders in Congress are following suit.
"I think the (incoming) Bush administration has failed the first test. And that was reaching out to people of color when it comes to the judicial system. Because when he nominated Sen. Ashcroft, he demonstrated that he does not plan up open up the judicial system in this country to people of color," Rep. James E. Clyburn, D-S.C., the Congressional Black Caucus leader, told CBSNews.com in an interview last week.
Ashcroft has countered the criticism of his civil rights record by noting he supported 23 of the 26 nominations of black judges that came up for a vote during his Senate tenure.
The political stakes are extremely high for the president-elect, who just lost his labor nominee, Linda Chavez. He can ill-afford to lose another nomination fight if he's to keep his Cabinet-building - and nascent administration - on track.
But Ashcroft's nomination is anything but dead. Powerful GOP senators are lining up behind him and drawing battle lines.
"I think he treated Judge White with fairness. I mean, I could see why people could be on either side of that issue," said Sen. Orrin Hatch, R-Utah, last week.
White's confirmation was defeated in the Senate along party lines, and ever since, blacks have vowed revenge for what they considered a racially biased vote. Their first payback was at the polls last November when African-Americans nearly tripled their turnout to defeat Ashcroft's bid for re-election as U.S. senator from Missouri.
Ashcroft had opposed White because of his actions in a case involving Vietnam veteran Jimmy Johnson, who was sentenced to die for a string of cop killings. On appeal, White was the lone Missouri justice to votagainst the death penalty, even though he had upheld 70 percent of all the other death sentences he reviewed a fact that Ashcroft chose to overlook.
"We don't need judges with a tremendous bent toward criminal activity," Ashcroft said of White on the Senate floor.
Senators are known for supporting nominations of former colleagues, and the Rev. Jackson's comments are aimed at that tradition.
The Senate's top Republican, Trent Lott, R-Miss., said he still believes Ashcroft will be confirmed and hinted that a major challenge of his nomination might have damaging consequences.
"A concerted effort to 'Bork' John Ashcroft would not be well received, and I do not believe his Democratic Senate colleagues would be inclined to do that,'' said Lott. "It would really sour a major opportunity we have here now to work together.''
Lott's "Bork" reference was to conservative jurist Robert Bork, whose Supreme Court nomination by President Reagan was rejected by the Senate after aggressive attacks by liberal organizations.