Rep. Carolyn Maloney Carolyn Bosher MaloneyGovernment watchdog recommends creation of White House cyber director position Top Democrats call for DOJ watchdog to probe Barr over possible 2020 election influence House panel advances bill to ban Postal Service leaders from holding political positions MORE (D) on Sunday endorsed her colleague from New York, Sen. Kirsten Gillibrand Kirsten GillibrandSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Suburban moms are going to decide the 2020 election Jon Stewart urges Congress to help veterans exposed to burn pits MORE (D-N.Y.), for president.

"I am proud to endorse my friend @SenGillibrand to be our next President and the nation's first woman President," Maloney wrote on Twitter.

"I saw her tenacity when we fought together to pass the 9/11 Health bill and know she has what it takes to defeat Trump."

I am proud to endorse my friend @SenGillibrand to be our next President and the nation's first woman President. I saw her tenacity when we fought together to pass the 9/11 Health bill and know she has what it takes to defeat Trump. https://t.co/R11qUOLC2A — Rep. Carolyn B. Maloney (@CarolynBMaloney) March 17, 2019

Gillibrand officially announced her 2020 candidacy on Sunday after having formed an exploratory committee in January.

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The 52-year-old New York lawmaker joins a crowded and diverse pool of Democratic candidates vying to take on President Trump Donald John TrumpOmar fires back at Trump over rally remarks: 'This is my country' Pelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Trump mocks Biden appearance, mask use ahead of first debate MORE in 2020. She is one of six women who have announced runs so far.

Maloney's endorsement is Gillibrand's first so far from a sitting member of Congress, according to Politico.

Two representatives from New York, Kathleen Rice Kathleen Maura RiceHillicon Valley: Simulated cyberattack success | New bill for election security funding | Amazon could be liable for defective products Lawmakers introduce bill to help election officials address cyber vulnerabilities House lawmakers to launch probe into DHS excluding NY from Trusted Traveler Program MORE (D) and Sean Maloney Sean Patrick MaloneyAudience cheers Maloney for getting Sondland to say he assumes Trump 'would benefit' from investigation into Bidens Applause breaks out after Vindman says he's not worried about testifying because 'this is America' Live coverage: House holds third day of public impeachment hearings MORE (D), have endorsed former Rep. Beto O’Rourke (D-Texas) in the 2020 race.