In her remarks Tuesday night, Feinstein noted somewhat mysteriously that if Trump didn't redeem himself, "there are things that could happen that I don’t think it would be responsible for me to talk about here.”
A member of the Senate Intelligence Committee investigating Russia's meddling in the 2016 election, Feinstein downplayed talk that Trump would be impeached or resign.
“This man is going to be president most likely for the rest of this term," she said. "I just hope he has the ability to learn and change. If he does, he can be a good president.”
That sentiment didn't go over well when Democratic consultant Garry South was told about it.
"He’s irredeemable," South said of Trump. "You gotta call a spade a spade. He’s not going to change. There is no Trump 2.0."
As to Feinstein's urging patience, South added that "waiting for Trump to become a good president is like leaving the landing lights on for Amelia Earhart. She ain't coming back, and he ain't gonna change. He's a bad president because he's a terrible human being. Pure and simple."
Feinstein's comments seem especially tone-deaf coming just days after a poll by David Binder Research found that 60 percent of California voters -- including 20 percent of Republicans -- think it would be best for the nation if Trump leaves office before the end of his term.
Feinstein is facing re-election next year, and so far no credible Democrat has announced a challenge. Her seniority in the Senate, her fundraising prowess, her high name recognition in the state and her strong approval ratings make challenging her a less-than-appealing task.
Still, South, the Democratic consultant, says Feinstein's comments are a reminder of how far the party has moved to the left since she was first elected in 1992.
"I think it's gonna raise some eyebrows among the base," he said.
On health care reform, Feinstein said she favored a public option for health care, but that's unlikely to satisfy supporters of single payer, also known as "Medicare for All."
RoseAnn DeMoro, executive director of National Nurses United and a fierce advocate of single-payer health care, says the public option won't solve problems with the Affordable Care Act.
"The public option bears more in common with fool's gold," DeMoro said recently. "It may look shiny, but it will still leave you broke."
Feinstein also reminded the audience that she opposed NAFTA back in 1993 and thinks it needs to be changed or renegotiated.
"I didn't believe it was a great deal for California," she said of her feelings at the time. "There was a great sucking sound of pushing things into Mexico."
On Trump's pardon of controversial Arizona sheriff Joe Arpaio, Feinstein said, "He was a terrible sheriff." She called the pardon "a stupid thing to do."
At the event, Feinstein was questioned by her former campaign treasurer and longtime friend Ellen Tauscher, who represented the East Bay in the House of Representatives from 1997 to 2009.
The questions, like "What are your priorities?" and "What's your secret to bipartisanship?" were friendly. When asked "What are your plans for the next five to 10 years?," a gentle reference to her political future, Feinstein said simply "next question." Tauscher obliged and moved on.
The senator, who is 84 and the oldest member of the U.S. Senate, is widely expected to run for another term next year.
Note: This story was updated after it originally appeared to include comments from Sen. de León and Sen. Feinstein's response. We also clarified the difference between the "single payer" and the "public option" Feinstein supports.