“It's important to know when it's not your time,” she said in a video posted to her Twitter account.

Democratic presidential candidate Sen. Kirsten Gillibrand speaks at the Presidential Gun Sense Forum on Aug. 10, 2019, in Des Moines, Iowa. Charlie Neibergall / AP

By Jane C. Timm | NBC News

Sen. Kirsten Gillibrand, D-N.Y., announced Wednesday that she is ending her White House bid. She is the first senator to drop out of the crowded Democratic primary.

Gillibrand, who championed the issues of women and families on the trail, has been campaigning for the 2020 Democratic nomination since January, but she struggled to make a dent in the race. She lacked both the polling and required number of donors needed to qualify for the third Democratic debate next month, as the Wednesday night deadline loomed.

"I know this isn't the result we wanted, we wanted to win this race, but's important to know when it's not your time,” she said in a video posted to her Twitter account. “I believe I can best serve by helping to unite us to beat Donald Trump in 2020."

Today, I am ending my campaign for president.

I am so proud of this team and all we've accomplished. But I think it’s important to know how you can best serve.

To our supporters: Thank you, from the bottom of my heart. Now, let's go beat Donald Trump and win back the Senate. pic.twitter.com/xM5NGfgFGT

— Kirsten Gillibrand (@SenGillibrand) August 28, 2019

She ends her campaign with $800,000 cash on hand, her campaign said in an email to reporters, and plans to relaunch her Off the Sidelines PAC by October. The PAC raised millions in the 2014 and 2016 cycles to support women running for office, and her campaign said Wednesday that Gillibrand plans to raise and invest at least $1 million into electing women in 2020.

She is the first woman to drop out — in a year that saw a record-smashing number of women running for president — and joins a handful of others who have already ended their bids. Washington Gov. Jay Inslee, Massachusetts Rep. Seth Moulton and former Colorado Gov. John Hickenlooper left the Democratic race in recent weeks, while California Rep. Eric Swalwell ended his campaign in early July.

"I can't wait to keep speaking out, marching, and fighting with you," she said in the video.

Senior Gillibrand aides told NBC News that the senator decided with her family that unless she was able to secure a last-minute spot on the September debate stage, she would accept that she did not have a path to the party's nomination. After two newly released polls Wednesday morning showed no bump in support, she taped the video message and later informed staff of her decision at an all-team meeting at her campaign headquarters in Troy, New York, the aides said.

Gillibrand had spent much of the last week on the West coast, aggressively trying to meet the debate qualifications. She launched a million-dollar ad buy to help boost her state-based name identification and increased her television interviews asking for $1 donations, to little success.

A fierce critic of President Donald Trump, Gillibrand leaned into gender and motherhood, pitching a paid family leave policy, and talked up her roots in rural, upstate New York with a plan for revitalizing rural America. She called for getting money out of politics with a publicly-funded election plan, and she made LGBTQ rights a core part of her campaign, spending time with drag queens in Des Moines, Iowa.

Still, questions of "electability" dogged her from the start, and she was frequently asked about her decision to call for former Sen. Al Franken of Minnesota to resign after he faced a string of sexual misconduct allegations. Gillibrand was the first of Franken's Democratic colleagues in the Senate to publicly urge him to step down, which he did in 2017.

Campaign manager Jess Fassler said in a memo emailed to reporters that Gillibrand released 15 policy proposals in total, including plans on climate change, reproductive rights, public service and gun violence.

Her rivals for 2020 nomination — including her colleagues in the Senate — met the news of her decision with flattering statements. Sen. Kamala Harris, D-Calif., called her a "champion" while Sen. Cory Booker, D-N.J., said he'd miss running into her on the trail. Rep. Tim Ryan, D-Ohio, said he hoped they could share a whiskey soon. Sen. Elizabeth Warren thanks her for her "unwavering commitment to fighting for women—from reproductive rights to paid leave."

"Your voice has been strong and clear, and your determination is always on display. I'm proud to keep fighting alongside you," Warren said.

Trump appeared to mock her withdrawal from the race.

"I’m glad they never found out that she was the one I was really afraid of!" he wrote in a tweet.