It was a chilly December evening—the end of a long day, at the end of a long year—and Kirsten Gillibrand, riding in the front passenger seat of her family's minivan, was hoping she'd left her problems at work.

She was headed to a school open house, enjoying a rare moment of parental normalcy with her husband, Johnny, and their 14-year-old son, Theo—all of them eager to solve the vexing question of where Theo should attend high school next year. Gillibrand had struggled to give the decision her full attention. Since Donald Trump's election, her job as the junior Democratic senator from New York had become all-consuming.

Gillibrand hadn't been sleeping well, so intense were her anxiety dreams. And yet the work had also re-energized her. She'd blasted Trump on just about everything—on things he had done, like his travel bans, and on things he hadn't gotten done (“Has he kept any of these promises?” she'd asked a crowd in New York. “No. Fuck no!”). She'd become such a persistent bulwark against Trumpism that just that very morning she'd prompted the president to lash out at her.

Gillibrand had been with some fellow senators, in a weekly Bible-study meeting, when her chief of staff phoned her with urgent news of a not-very-Christian nature. Trump had just issued a tweet that she should see: “Lightweight Senator Kirsten Gillibrand, a total flunky for Chuck Schumer and someone who would come to my office ‘begging’ for campaign contributions not so long ago (and would do anything for them), is now in the ring fighting against Trump.”

Gillibrand was long accustomed to the boorish behavior of some of her male colleagues. Once, in the House of Representatives gym, a fellow member of Congress complimented her, “Good thing you're working out, because you wouldn't want to get porky!” On another occasion, a senator squeezed her waist and said, “Don't lose too much weight, now. I like my girls chubby!” But Trump had taken such behavior to a new low. As a shaken Gillibrand told her colleagues in the Bible study, the president of the United States “basically just called me a prostitute.” She asked them to pray for her. The rest of the day was a mess as Gillibrand dealt with reaction to what she called Trump's “sexist smear.”

Now, in the sanctuary of the minivan, she could put that aside. Gillibrand turned on the radio. The top story was about her and Trump. She immediately switched it off.

“What was that, Mom?” Theo asked.

“Oh, the president, you know, tweeted against me today,” Gillibrand replied, trying to sound casual.

“Well, what did he say?”

“Oh, he basically said Mom's doing a bad job, and I said, ‘I disagree.’ ”

Theo pressed her for details, but Gillibrand wasn't about to tell her son that the president had likened her to a prostitute. “Well, that's really all I'm going to tell you right now,” she finally told him.

Relating the story to me several months later, Gillibrand still felt a rush of disbelief. “I couldn't even tell my children, because it was X-rated and so inappropriate,” she told me. “I don't want my children to even think in those terms, so I couldn't even describe what the president said.”

Having to shield one's kids from the vulgar attacks of the president is the strange sort of task that a working mother takes on these days when she also happens to be a leader of the anti-Trump resistance. But Gillibrand's growing notoriety as a Trump adversary confers its benefits, too. Once considered a hardworking but hardly scintillating politician, Gillibrand has suddenly become a bona fide political star—turning up everywhere from Stephen Colbert's late-night chair to Al Sharpton's Harlem headquarters.