Several Democrats running for the party's 2020 nomination on Friday criticized 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's new policy prohibiting transgender troops from serving in the military unless they serve under their biological sex.

The controversial measure, which ends the previous policy under former President Obama allowing transgender people to serve openly, went into effect on Friday.

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Sens. Kamala Harris Kamala HarrisButtigieg stands in as Pence for Harris's debate practice First presidential debate to cover coronavirus, Supreme Court Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (Calif.), Cory Booker Cory Anthony BookerBipartisan praise pours in after Ginsburg's death DHS opens probe into allegations at Georgia ICE facility Democratic lawmakers call for an investigation into allegations of medical neglect at Georgia ICE facility MORE (N.J.) and Elizabeth Warren Elizabeth WarrenHarris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda Judd Gregg: The Kamala threat — the Californiaization of America GOP set to release controversial Biden report MORE (Mass.), as well as South Bend, Ind., Mayor Pete Buttigieg Pete ButtigiegButtigieg stands in as Pence for Harris's debate practice Hillicon Valley: FBI, DHS warn that foreign hackers will likely spread disinformation around election results | Social media platforms put muscle into National Voter Registration Day | Trump to meet with Republican state officials on tech liability shield Facebook takes down Chinese network targeting Philippines, Southeast Asia and the US MORE, were among those who spoke out against the measure on Twitter, with many of them calling it a ban.

The Pentagon denies the policy, a revamped version of a stricter one unveiled earlier, is a ban.

The department argues currently serving transgender service members or anyone who has already signed an enlistment contract can continue to serve openly, and point to the carveouts for transgender people willing to serve under their biological sex.

But the policy has been opposed by most Democrats.

"To the transgender Americans who serve in our Armed Forces: You deserve better," Harris wrote on Friday. "We stand with you in opposing Trump’s reprehensible, vile, and discriminatory ban."

To the transgender Americans who serve in our Armed Forces:



You deserve better.



We stand with you in opposing Trump’s reprehensible, vile, and discriminatory ban.https://t.co/jAYb8EnnJB — Kamala Harris (@KamalaHarris) April 12, 2019

"The #TransMilitaryBan must be defeated. To the thousands of transgender patriots serving in our military, we are so grateful for your service and will fight this ban with you," Booker wrote. "Make no mistake: an attack on the transgender community is an attack on us all."

The #TransMilitaryBan must be defeated. To the thousands of transgender patriots serving in our military, we are so grateful for your service and will fight this ban with you.

Make no mistake: an attack on the transgender community is an attack on us all. https://t.co/CKAErfvR98 — Sen. Cory Booker (@SenBooker) April 12, 2019

Buttigieg, who is a veteran, encouraged his followers to "ask how we could stand for courageous service members to have their careers destroyed by a president who pretended to be disabled in order to avoid serving when it was his turn," referring to Trump's five draft deferments during the Vietnam war due to bone spurs.

Read this story and ask how we could stand for courageous service members to have their careers destroyed by a president who pretended to be disabled in order to avoid serving when it was his turn. As of today, this is not theoretical. https://t.co/JhY5x6Tzp3 — Pete Buttigieg (@PeteButtigieg) April 12, 2019

"Let me be very clear: If someone can handle the job, they should be allowed to serve—regardless of how they identify or who they love," Warren tweeted. "We’ll stand with service members and fight this cruelty with everything we’ve got."

Let me be very clear: If someone can handle the job, they should be allowed to serve—regardless of how they identify or who they love. We’ll stand with service members and fight this cruelty with everything we’ve got. https://t.co/cKPBglSBrG — Elizabeth Warren (@ewarren) April 12, 2019

Other Democratic presidential candidates who denounced the policy change include 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 (N.Y.), former Housing and Urban Development Secretary Julián Castro and Rep. Tim Ryan Timothy (Tim) RyanNow's the time to make 'Social Emotional Learning' a national priority Mourners gather outside Supreme Court after passing of Ruth Bader Ginsburg Lincoln Project hits Trump for criticizing Goodyear, 'an American company' MORE (Ohio)

Our troops deserve a Commander in Chief who fights for them as fiercely as they fight for this country. President Trump's transgender military ban, taking effect today, proves he fails that standard. As president I will end this. https://t.co/Ddn3PFWugY — Kirsten Gillibrand (@SenGillibrand) April 12, 2019

To the transgender troops who proudly serve our country every day: this fight isn't over and we will continue to stand with you to oppose this discriminatory ban. #TransMilitaryBan #FightTheBan #OneNationOneDestinyhttps://t.co/0xnVwaHTfy — Julián Castro (@JulianCastro) April 12, 2019