The tenacious 46-year-old just may prevail.
"She has spunk. She is not afraid," says former New York Gov. David Paterson, who stunned the political world in January 2009 when he appointed the little-known, two-term congresswoman to replace Sen. Hillary Rodham Clinton when she was tapped by President Barack Obama to be secretary of state.
In a headline-grabbing turn of events, a child of Camelot, Caroline Kennedy, bowed out of contention. The Democratic governor settled on a child of tough Albany, N.Y., politics, and Gillibrand entered the Senate as its youngest member.
Four years later, she is locked in a ferocious fight with some of the Senate's more authoritative voices on the military.
Earlier this year, outrage over high-profile cases of sexual assault in the military and increasing numbers of service men and women fearful about reporting the crimes forced Congress to press for significant changes in military law and how the services deal with the victims.
Senate Armed Services Committee Chairman Carl Levin, the six-term Michigan Democrat who is retiring next year, proposed far-reaching policy changes, with the support of the Pentagon's top brass.
But Gillibrand, chairwoman of the Armed Services personnel subcommittee, countered that the approach was wrong.
She is slowly and steadily building support for a proposal to strip commanders of their authority to prosecute cases of sexual assault, instead handing responsibility to seasoned military lawyers. She now has 44 backers, including Sens. Michael Bennet, D-Colo., and Mark Kirk, R-Ill., who signed on last week, as well as conservative Sens. Rand Paul, R-Ky., and Ted Cruz, R-Texas.
She's relentless in trying to attract support for the bill. Gillibrand telephoned Senate Republican leader Mitch McConnell on a Saturday. He hasn't taken a stand on either measure yet; nor has Senate Majority Leader Harry Reid, D-Nev.
As starting pitcher on the congressional women's softball team, Gillibrand used early morning practices to lobby her teammates.
The competing measures are set for a late summer showdown that already has deeply divided the Senate, pitting some of the newer Republicans and Democrats less deferential to the Pentagon's demands against Senate experts on defense. The fight crosses gender and party affiliations and in the last few weeks has touched off a furious competition, even by Capitol Hill standards, with dueling news conferences, testimonials from retired military and statements from former prosecutors-turned-senators.
The high-profile issue has helped add Gillibrand's name to chatter about 2016 presidential candidates, a notion she says she finds flattering. But in an interview, she says emphatically, "I hope I get to see Hillary Clinton sworn in as our next president, and I intend to help her get elected."
Earlier this year, lawmakers were furious after learning that a senior Air Force official had overturned the conviction of a lieutenant colonel after a jury found him guilty of aggravated sexual assault, and there was no further recourse, not even by top leaders at the Pentagon.
Other episodes at the U.S. Naval Academy and West Point, combined with a Pentagon report on a survey estimating that as many as 26,000 military members may have been sexually assaulted last year, spurred lawmakers to act. The survey said thousands of victims were still unwilling to come forward despite new oversight and assistance programs aimed at curbing the crimes.
Gillibrand's measure would remove commanders from the process of deciding whether serious crimes, including sexual misconduct cases, go to trial. That judgment would rest instead with seasoned trial lawyers who have prosecutorial experience and hold the rank of colonel or above.
"The chain of command is really an impediment for solving it because it's resulting in underreporting, no transparency, no accountability," Gillibrand said in an interview last week. "The crux of the issue is objectivity. They (victims) don't believe the commanders can be objective, that commanders either know the victim or know the perpetrator or have a reason to support the perpetrator, who is more senior, more decorated, gone on more missions than the victim."
She said "that lack of objectivity is what creates the fear that justice won't be done."
Levin's proposal, which was adopted by the Armed Services panel on a 17-9 vote, is designed to increase pressure on senior commanders to prosecute sexual assault cases by requiring a top-level review if they fail to do so. He also would make it a crime to retaliate against victims who report a sexual assault and also calls on the Pentagon to relieve commanders who fail to create a climate receptive for victims.
"The power to initiate court martials is perhaps the strongest weapon commanders have," Levin told reporters in a conference call this past week. He argued that to remove that power — as Gillibrand's idea would do — "actually weakens the effort to change the climate and bring the perpetrators to justice."
Levin has the support of Sens. Claire McCaskill, D-Mo., and Kelly Ayotte, R-N.H., former prosecutors, as well as Sen. Lindsey Graham, R-S.C., a member of the Air Force Reserves.
Graham said he's not willing to push commanders aside on the matter and replace their judgment with that of a judge advocate general, a position he once held in the armed forces. "I think this is an issue that commanders need to be held accountable for rather than removed from," he said.
The issue has touched off a flurry of "myth vs. fact" sheets and letters from advocacy groups and Pentagon leaders in the weeks leading up to expected September votes on the proposals, likely the most contentious issue in the debate over the sweeping defense policy bill.
The National Task Force to End Sexual and Domestic Violence Against Women, on behalf of 37 organizations, endorsed Gillibrand's effort, saying: "An impartial prosecutor, making decisions based on the facts of the case, will embolden survivors to report." Adm. James Winnefeld, vice chairman of the Joint Chiefs of Staff, said in a July 23 letter to Levin that "commanders recognized the need to hold service members accountable for their crimes both for the sake of justice, and to preserve good order and discipline."
Late Friday, in a clear reflection of concern about the outcome, Sen. Jim Inhofe of Oklahoma, top Republican on the Armed Services Committee, sent a letter to all Senate Republicans warning that taking the power from commanders would be a "grave mistake." His letter criticized the misconceptions that have emerged.
Connecticut's former attorney general, Democratic Sen. Richard Blumenthal, has backed Gillibrand's effort, as has longtime Iowa Republican Sen. Charles Grassley, who says simply: "The status quo is not working, and we need to shake it up."
Gillibrand has pushed hard since arriving in the Senate. A wife and mother of two young boys, Theo, 9, and Henry, 5, she handily won in 2010 and again last year when she sought a full six-year term.
Former Sen. Joe Lieberman, I-Conn., recalls the persistence she displayed in trying to get health benefits for first responders to the Sept. 11 terror attacks and persuading the military to drop its decades-old policy of barring gays from serving openly in the services.
He remembers when a senator "came up to me and said, 'Look I know you're for this. I'm thinking about it. Please tell Kirsten Gillibrand to stop pestering me about it. She's killing me.'"
Fellow New York Democrat, Rep. Joe Crowley, calls her dogged. "It's kind of what we expect in New York," he says. Rep. Steve Israel, D-N.Y., describes Gillibrand as a "pit bull."
Paterson, who says he considered naming current New York Gov. Andrew Cuomo and Israel before picking Gillibrand, was widely criticized for the selection of the largely unknown upstate lawmaker.
"She's achieved way beyond my greatest expectations," he says.
Follow Donna Cassata on Twitter: http://twitter.com/DonnaCassataAP
Copyright 2013 The Associated Press.