(CNN) As senators grappled with how to handle the explosive allegations of sexual assault against Supreme Court nominee Brett Kavanaugh, Sen. Dianne Feinstein found herself in the center of the political storm.

As the sole Senate confidant of the woman accusing Kavanaugh, she was singled out Monday on the right by President Donald Trump and Senate Majority Leader Mitch McConnell -- who questioned the eleventh-hour revelation -- while being criticized from the left by her upstart Democratic challenger, Kevin de León, for keeping such serious allegations under wraps.

The criticism was an ironic twist in the lengthy political career of California's senior senator, who was the first female senator elected to represent the Golden State and one who has long been heralded as a champion of women's rights.

Ever the enigma, Feinstein -- who was elected in 1992's "Year of the Woman," in the wake of the Anita Hill hearings -- chose to keep secret the allegations of Christine Blasey Ford, the woman who says Kavanaugh pinned her down on a bed at a high school party in the 1980s, and clapped his hand over her mouth as he tried to assault her. Kavanaugh maintains that the incident never happened.

In an election year dominated by the fallout from the #MeToo movement, and at a time when the Senate was deciding the fate of the most consequential Supreme Court nominee in decades, Feinstein resolutely stood by her promise of confidentiality to Ford.

Feinstein, the ranking Democratic member of the judiciary committee, did not raise the issue with Kavanaugh in their private meeting. She did not tell her judiciary committee colleagues about the matter until The Intercept reported details of the incident last week. At that point, Feinstein forwarded the letter detailing Ford's account to the FBI and asked for an investigation.

As the story was unfolding last week, a number of Democratic operatives privately said they were stunned Feinstein had unilaterally decided not to share the information with her Democratic colleagues -- depriving them of the chance to question Kavanaugh during the judiciary committee hearings. Had the allegations not leaked to the press, they noted, Kavanaugh might have sailed through the confirmation process without having to answer to the charges.

California State Senate President Kevin de León, Feinstein's Democratic challenger in November, accused her of a "failure of leadership" for waiting "nearly three months to hand this disqualifying document" -- the July 30 letter -- "over to the federal authorities."

On Monday, the Republicans piled on. Trump questioned why Feinstein did not confront Kavanaugh about the accusations in their private meeting.

"One thing I will say is that, as I understand it, Judge Kavanaugh spent quite a bit of time with Sen. Feinstein, and it wasn't even brought up at that meeting," Trump said Monday. "And she had this information. So you would have thought, certainly, that she would have brought it up at the meeting, not wait until everything is finished and then have to start a process all over again."

McConnell, the Senate Republican Leader, suggested she kept them under wraps for maximum political affect as the Senate was coasting toward approving Kavanaugh's nomination.

In the midst of the controversy, Feinstein has not sought the spotlight, or felt the need to explain her actions -- perhaps because her prospects of re-election in November are so strong. Feinstein declined to be interviewed by CNN about her decision-making process Monday.

The California Senator is no stranger to criticism. Over the years, her allies say, she has learned to follow her own compass while taking the political darts in stride.

Feinstein reflected on the lessons she'd learned as a woman in politics in a book entitled "Nine and Counting: The Women of the Senate," which was published in 2001.

"If you are a woman who is meant to do this, you have to know that it will be a solitary road, and often lonely," Feinstein said in one passage of the book. "I choose to campaign alone. That's okay with me. Historically, our role models have always been strong, solitary women. It's what is meant to be."

Feinstein stands by her actions

Sources familiar with her thinking said she felt duty-bound to protect the victim's right to control her own story. That meant respecting Ford's request for confidentiality at all costs — even if it would have been to Democrats' political advantage to derail Kavanaugh's nomination.

Over the weekend, Feinstein released a statement saying she had always believed it was "Mrs. Ford's decision whether to come forward publicly" and that she viewed the allegations as "extremely serious" -- ones that "bear heavily on Judge Kavanaugh's character."

"However, as we have seen over the past few days, they also come at a price for the victim," Feinstein said in the statement. "I hope the attacks and the shaming of her will stop and this will be treated with the seriousness it deserves."

Her aides said she is looking forward, rather than backward, as the Senate moves toward a closer examination of the allegations at hearings on Monday.

On the campaign trail, Feinstein's handling of the incident created another opening for De León, who has repeatedly argued that California needs a fresh voice in the US Senate — someone who will embrace the more confrontational style of Democratic activists in the age of Trump.

In contrast with the forceful and sometimes disruptive performance of Feinstein's Democratic Senate colleagues like Kamala Harris and Cory Booker during the judiciary committee hearings on Kavanaugh's nomination, De León charged that Feinstein "politely pantomimed her way" through the hearing "without a single question about the content of Kavanaugh's character."

Former California Sen. Barbara Boxer, Feinstein's longtime Democratic colleague, dismissed De León's attacks as absurd.

"She is very thoughtful, very measured, and very thorough," Boxer said in an interview with CNN Monday.

"Sen. Feinstein was asked by the attorney — 'Please whatever you do, keep this confidential.' It's come out, and there's plenty of time to deal with it," Boxer said. "Dianne is getting criticized for no action. That's not true. She gave the information to the FBI, telling them to respect the woman's anonymity, and eventually she gave it to her colleagues on the committee."

"The reason that she does this — is that is who she is," Boxer said. "She's authentic. At the end of the day, she's fighting for women's equality."

Ford 'very satisfied' with Feinstein

One of the strongest defenses of Feinstein's actions has come from Ford's lawyer, Debra Katz, who said Feinstein and Ford first spoke shortly after Feinstein received the hand-delivered letter on July 30.

"She is very satisfied with how Dianne Feinstein handled this allegation," Katz said on CBS Monday morning. Ford "did have a conversation with the senator, who made it clear that she thought these allegations were important, and that they were serious, and her staff checked in with us routinely."

In an interview with CNN, Katz said the characterization that Feinstein sat on the letter was unfair.

"In this moment, victims need to be able to control when and whether their stories become public," Katz said on CNN Monday. "She went to her senator because she had information that she thought was very important that had bearing on the fitness and character of this nominee."

Over the ensuing months, Katz said Feinstein and her aides were eager to have Ford "come forward if she felt comfortable coming forward."

"There was no effort to dissuade her from coming forward," Katz said. "This was entirely this woman's decision. And I think that was appropriate. I think that's how victims of trauma and sexual violence must be treated."