[14] Following the election of Donald Trump in November 2016, Harris was named as part of the "Hell-No Caucus" by Politico in 2018, along with Senators Cory Booker, Kirsten Gillibrand, Elizabeth Warren, and Bernie Sanders, given she voted "overwhelmingly to thwart [Trump's] nominees for administration jobs", such as with Rex Tillerson, Betsy DeVos, and Mike Pompeo; all the senators in this group were considered potential 2020 presidential contenders at this point in time.

[17][18][19] The following month, it was confirmed that Harris was expected to make an official announcement around Martin Luther King Jr. Day regarding the 2020 election.

[21] Prior to and during her presidential campaign, an online informal grouping using the hashtag #KHive formed to support her candidacy and defend her from racist and sexist attacks.

"[26] On Martin Luther King Jr. Day, January 21, 2019, Harris announced on Good Morning America that she would be seeking the Democratic presidential nomination.

[33] An overflow crowd of over 20,000 attended her formal campaign kickoff event at Frank Ogawa Plaza in her hometown of Oakland, California, on January 27.

[36] On January 28, Harris introduced herself as a 2020 presidential candidate in a CNN town hall at Drake University in Des Moines, Iowa.

[44] Harris also secured the support of former Massachusetts Attorney General Martha Coakley and Latina labor rights activist and co-founder of the United Farm Workers union, Dolores Huerta.

[45][46] Harris came under criticism when, in February 2019, she immediately believed the Jussie Smollett hate crime hoax while the affair had already been strongly questioned by the Chicago Police Department.

The Daily Beast asserted this was representative of her supposed "habit of making flip comments, and tending to latch on to narratives that confirm her preferred political worldview".

[47][48] In March, Harris headlined a fundraiser from high-profile Hollywood donors at the home of American filmmaker J. J. Abrams and Katie McGrath.

[52] On May 5, Harris gave a speech at the Fight for Freedom Fund Dinner of the Detroit Branch NAACP in which she pledged that her administration would "hold social media platforms accountable for the hate infiltrating their platforms, because they have a responsibility to help fight against this threat to our democracy" and referred to 2018 as the "deadliest year on record for domestic terrorism" since the 1995 Oklahoma City bombing.

[76] On July 12, Harris appeared on The View, where she stated her position on illegal immigration was treating the subject as a "civil enforcement issue" that was concurrent with a secure border and not treating individuals who entered the U.S. illegally like criminals; before she stated her intent to discontinue multiple practices of the Trump administration as it related to the subject.

The proposal gathered praise from former U.S. Health and Human Services Secretary Kathleen Sebelius but drew immediate criticism from supporters of Bernie Sanders.

[79] On July 31, Harris defended her health care plan from claims by Joe Biden that it would cost $3 trillion and eliminate employer-based insurance.

[80] Congresswoman Tulsi Gabbard attacked Harris over her record as Attorney General, notably her past positions on marijuana, cash bail, and parole reform.

Both failed in this regard; "Harris tried to land a few jokes and zingers (including an awkward line to Biden about how 'yes we can' do gun control), but she seemed to be the only one laughing at them.

"[84] Jonathan Easley of The Hill complimented Harris's overall performance as she appeared "more at ease in a debate where she didn't seem pressured to be leading the attacks against Biden.

[87] Harris was memorably caught on a hot mic declaring to Hawaii Senator Mazie Hirono "I'm fucking moving to Iowa.

[95][96] In addition, she earned the support of the Black Caucus of the Michigan Democratic Party and civil rights attorney Benjamin Crump.

[99] On October 15, the fourth debate of the primary season was held at Otterbein University in Westerville, Ohio, hosted by CNN and The New York Times.

Harris objected to the fact that students at Benedict College were not permitted to attend and were instructed to remain in their dorms during the event, stating:[103] "Donald Trump is a lawless President.

[108] On November 8, Harris was the first candidate to hold a town hall with the rank and file members of Culinary 226 after receiving an exclusive invitation earlier that week.

[110] On November 20, 2019, the fifth debate of the primary season was held at Tyler Perry Studios in Atlanta, GA, hosted by MSNBC and The Washington Post.

She further remarked that candidates had been taking for granted the constituencies that had been "the backbone of the Democratic Party" by showing up in a black church close to election time in the following statement:[111] "...

Another viral moment occurred when Vice President Joe Biden mistakenly remarked that the "only African-American woman that had ever been elected to the United States Senate" had endorsed him,[113] to which Harris laughed, "No, that's not true.

[119] On November 27, Harris spent the Thanksgiving holiday in Des Moines, Iowa with fellow candidates Amy Klobuchar and Cory Booker.

She attended the Turkey Trot downtown and visited the Corinthian Gardens apartment, where Harris campaigned for President Barack Obama in 2008.

[124] Harris was the first office-holding Indian/Caribbean woman to seek the Democratic nomination for president, the first two being U.S. representative Shirley Chisholm in 1972 and U.S. senator Carol Moseley Braun in 2004.

A New York Times report indicated that Harris, along with former national security advisor Susan Rice, senator Elizabeth Warren, and Michigan governor Gretchen Whitmer, were on Biden's final shortlist.

On November 7, Biden and Harris were declared the winners, although incumbent president Donald Trump refused to accept the results of the election, making unsubstantiated claims of voter fraud.