Sen. Kamala Harris, D-Calif., said Thursday that "voters will decide" if newly announced presidential candidate Beto O'Rourke will be her primary competition in a crowded field of Democrats vying for the party's nomination in 2020.

"Oh, I think the voters will decide," she told NBC News' Peter Alexander in an interview on MSNBC's "Andrea Mitchell Reports," adding, "the more the merrier."

Just hours after the former congressman from Texas made his presidential bid official, Harris' campaign sent out a fundraising email with the subject line "Beto O'Rourke."

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The email notes the record number of women and people of color in the running for the Democratic nomination so far and quotes Harris saying, "I look forward to engaging in substantive debates with each of these candidates—including the newest to join the race today, Beto O'Rourke."

In a Vanity Fair interview published Wednesday — in which he hinted at his decision to run but did not announce it — O'Rourke acknowledged that a foray into the most diverse field of candidates in history could be met with some resistance.

"I totally understand people who make a decision based on the fact that almost every single one of our presidents has been a white man and they want something different for this country. And I think that’s a very legitimate basis upon which to make a decision," he told the magazine.

Asked to respond to that quote, Harris said that "the American public is smart enough to make decisions based on who speaks their truth, who has a proven record of producing, who knows how to fight for Americans and working people and it is on that basis that our country will elect its next president."

Harris, a former prosecutor, also said she supported California Democratic Gov. Gavin Newsom's plan to halt the use of the death penalty in the state, and reiterated that she is personally opposed to the death penalty.

"This is a sentence that has been disproportionately applied against people of color and in particular black and brown men in this country. And it is also not a deterrent to the extent people would argue," she said.