Democratic Sen. Kamala Harris kicked off her campaign for the presidency on Sunday with an energetic rally of thousands of supporters in her hometown of Oakland, California, framing her candidacy as an effort to restore fundamental American values she believes are under attack.

"We are at an inflection point in the history of our world. We are at an inflection point in the history of our nation. We are here because the American dream and our American democracy are under attack and on the line like never before," Harris said. "We are here at this moment in time because we must answer a fundamental question: Who are we? ... Who are we as Americans?"

She declared that "under this administration, America's position in the world has never been weaker" with "foreign powers infecting the White House like malware."

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The 54-year-old freshman lawmaker announced her bid for the Democratic nomination last week, becoming the fourth female candidate to wade into the already-crowded race.

An estimated 20,000 people crowded a plaza in front of Oakland City Hall, filing in shortly before 1 p.m. local time as musical acts performed and a young girl recited the pledge of allegiance. A pastor delivered an impassioned invocation before Harris was introduced by Libby Schaaf, the mayor of Oakland.

Sen. Kamala Harris speaks as she formally launches her presidential campaign at a rally in her hometown of Oakland, Calif., on Sun., Jan. 27, 2019. AP

Harris took the stage to the tune of Mary J. Blige at about 1:40 p.m., greeted by loud applause from the assembled supporters, many of whom waved signs emblazoned with her campaign slogan, "For the People."

The former California attorney general said she was "so proud to be a daughter of Oakland, California," noting she was born at a nearby hospital. She never mentioned President Trump by name, but vowed to challenge him directly, highlighting her work as a prosecutor to argue against the administration's immigration policies.

"Folks, on the subject of transnational gangs, let's be perfectly clear: The president's medieval vanity project is not going to stop them," Harris said, presumably referring to Mr. Trump's proposed border wall.

"When we have children in cages, crying for their mothers and fathers, don't you dare call that border security," she added later. "That's a human rights abuse."

The Republican National Committee was quick to return fire, with a spokesman saying Harris' "liberal policies are totally out-of-step with most Americans."

After graduating from law school in 1989, Harris returned to Oakland and worked for the Alameda County district attorney's office. In 2003, she defeated a two-term incumbent to become San Francisco district attorney, a position that had never been held by a woman or person of color.

Harris announced her presidential run last Monday on Martin Luther King Jr. Day after telegraphing her intentions for months. Elected to the Senate in 2016, Harris has used her perch on the powerful Judiciary Committee to quickly elevate her profile. She has laid out a plan to provide middle-class families with tax credits worth thousands of dollars. She wrote a new book published in early January laying out her life story and career as a prosecutor.

The daughter of Jamaican and Indian immigrants, Harris' campaign logo and promotional materials evoked the style used in the 1972 campaign of Shirley Chisholm, the first African American woman to run for the nomination of a major party.

Harris' campaign will have its headquarters in Baltimore, with a second location in Oakland.

Watch Harris' full remarks in the video below:

Sean Gallitz contributed reporting from Oakland.