Gillibrand, 52, has not seen great improvement in her polling numbers increase since her initial announcement, a benefit some opponents enjoyed after starting their campaigns. "Let's prove that fearless wins", Ms. Gillibrand said in her tweet.
In a two-and-a-half-minute video spot, Gillibrand said, "We need to remember what it feels like to be fearless".
The New York Democrat launched an exploratory campaign in January, announcing it on CBS' "The Late Show with Stephen Colbert", and has spent the past two months traveling to key states.
Playing off the "home of the brave" line of the national anthem, Gillibrand says: "Brave doesn't spread hate, cloud truth, build a wall - that's what fear does".
Her speech outside the Trump International Hotel and Tower in New York City will be next Sunday. Gillibrand reiterated her support for universal health care, paid family leave, tighter gun control regulations, the Green New Deal and other progressive reforms.
Says Gillibrand in the clip: Our anthem calls America 'the home of the fearless.' ...
Gillibrand has made a name in the Senate for her fierce advocacy for victims of sexual assault in the military, and for her sharp criticism of Mr. Trump.
She has also been an advocate of women's rights, including anti-sexual misconduct and equal treatment for women. "And its these fearless choices that inspire me to take on the fights others won't", Gillibrand says.
Gillibrand is the next prominent Democrat to enter the 2020 presidential race. Her positions became more liberal after she was appointed to fill the Senate seat vacated by Hillary Clinton when Clinton became Barack Obama's first secretary of state. President Donald Trump has has no reaction to his democratic challengers but Minnesota Senator Amy Klobucher said "I always like to say- may the best woman win". She has struggled to see her polling numbers increase in the wake of her initial announcement, a benefit some of her other opponents enjoyed after starting their campaigns. Kennedy said he hopes O'Rourke's visit is a sign that presidential candidates will be spending more time in Midwestern states than they did during the 2016 election cycle.
Republican strategist John Weaver called the tweet "vile".