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Representative Tulsi Gabbard, Democrat of Hawaii, resigned as a vice chairwoman of the Democratic National Committee on Sunday in order to endorse Senator Bernie Sanders for president.

The endorsement came a day after Hillary Clinton won the Democratic primary in South Carolina by a huge margin — she captured nearly 74 percent of the vote — in a signal of her support in the South right before several other Southern states vote in Tuesday’s primaries.

Ms. Gabbard explained her decision in a video on YouTube in which she said that, as a military veteran, she wanted the United States to avoid “interventionist wars of regime change.”

“As a veteran of two Middle East deployments, I know first hand the cost of war,” said Ms. Gabbard, one of the first female combat veterans to serve in Congress. “I know how important it is that our commander-in-chief has the sound judgment required to know when to use America’s military power and when not to use that power.

“As a vice chair of the D.N.C., I am required to stay neutral in democratic primaries, but I cannot remain neutral any longer,” she added. “The stakes are just too high. That’s why today I’m endorsing Senator Bernie Sanders to be our next president and commander in chief of the United States.”

Ms. Gabbard, while not mentioning Mrs. Clinton by name, went on to cast Mr. Sanders as being more interested in peace and as someone who would be better trusted with the lives of American troops. She also implied that Mr. Sanders had better foreign policy judgment than his rival.

“We need a commander in chief who has foresight, who exercises good judgment, and who understands the need for a robust foreign policy which defends the safety and security of the American people, and who will not waste precious lives and money on interventionist wars of regime change,” Ms. Gabbard said. “We can elect a president who will lead us into more interventionist wars of regime change, or we can elect a president who will usher in a new era of peace and prosperity.”

Ms. Gabbard, who was born in American Samoa and is the first Hindu elected to Congress, is seen as a young, rising star of the party but has publicly battled Democratic leadership. In October, Ms. Gabbard said she was uninvited from the first Democratic presidential primary debate by the chief of staff to Representative Debbie Wasserman Schultz of Florida, the chairwoman of the national committee, after Ms. Gabbard appeared on television and called for more debates.

At the time, the party’s leadership had been criticized for allowing only a limited number of debates, which some viewed as an effort to deny Mr. Sanders more time to confront Mrs. Clinton when she was ahead in polls. Ms. Wasserman Schultz has denied that Ms. Gabbard was uninvited from the debate.

Mr. Sanders welcomed Ms. Gabbard’s endorsement Sunday.

“Congresswoman Gabbard is one of the important voices of a new generation of leaders,” Mr. Sanders said in a statement. “As a veteran of the Iraq War she understands the cost of war and is fighting to create a foreign policy that not only protects America but keeps us out of perpetual wars that we should not be in.”

Ms. Wasserman Schultz praised Ms. Gabbard with a statement of her own. “As one of the first female combat veterans to serve in Congress and the first American Samoan and Hindu member of Congress, Congresswoman Gabbard is a role model who embodies the American ideal that anyone can dream big and make a difference,” Ms. Wasserman Schultz said. “She is also a colleague in Congress and a friend, and I look forward to continuing to work alongside her when our Party unites behind whoever emerges as our nominee.”