Sen. Elizabeth Warren, a 2020 presidential candidate, vowed on Monday to avoid any traditional political fundraisers with wealthy donors during the Democratic primaries but said she will go back to traditional fundraising during the general election when she's up against the GOP's "wealthy-wealthy donors" and "dark money."

Warren, who is reportedly looking to boost her online fundraising, posted on Medium that she intends to be the "best president money can't buy."

ELIZABETH WARREN SWEARS OFF 'BIG MONEY' FUNDRAISERS WITH WEALTHY DONORS

Politico ran the headline, "Warren creates purity test unseen in modern presidential politics."

A senior aide for Warren told the publication, "She is an outsider. She is a reformer. She is an anti-corruption candidate, and this is one of many steps she has taken to help cement that in the mind of voters. By not doing the traditional big-dollar finance program, she will have a lot more time than other candidates to focus on organizing in the early states and other priorities."

Warren appeared on MSNBC’s "All in With Chris Hayes" and was asked about the move. She claimed that avoiding these big-ticket events helps the candidate connect with the grassroots voters and build a strong foundation prior to the 2020 general election.

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She was questioned about her past that included reaching out to wealthy donors and putting together a sizable war chest of about $12 million. She indicated that the "big money" fundraiser avoidance would only apply to the primaries because Republicans will be "armed to the teeth" during the general election.

"They’ve got all of their donors, they're wealthy-wealthy donors; they've got their Super PACs; they’ve got their dark money; they’ve got everything going for them,” she said.

The Wall Street Journal reported that her campaign manager wrote in an email that she will conduct fundraising events, but they will be “pay-what-you-can.”

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The vow is the first of its kind among 2020 Democratic candidates. Warren acknowledged that the ever-growing Democratic primary field would likely outraise her due to her decision.

Fox News' Brooke Singman contributed to this report