A liberal grassroots activist group claims to have raised more than $500,000 in 24 hours to challenge vulnerable Republicans who voted for the GOP's plan to repeal and replace ObamaCare.

The group, Swing Left, has been touting its fundraising haul on Twitter as the donations pour in. And it noted in a release that $150,000 of that total was raised in the first hour after the Thursday afternoon vote.

Because of you we've raised half a million dollars in 24 hrs to unseat Republicans in 2018. You all are incredible. https://t.co/3qijskJNlG — Swing Left (@swingleft) May 4, 2017

Donors gave $100,000 specifically for the eventual Democratic challenger to Rep. Darrell Issa (R-Calif.), a top Democratic target who voted for the ObamaCare repeal bill.

"The House just passed Trumpcare with 35 votes from representatives in Swing Districts," the group writes in its fundraising appeal.

Swing Left touted donations as a chance to make GOP lawmakers "regret voting for Trump's disastrous agenda."

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Swing Left is attempting to mobilize Democrats to win over 65 identified swing districts — 48 Republican-held and 17 Democratic-held. On top of donations, it also seeks to spur volunteers to work in swing districts that they live near.

Jon Favreau, a former speechwriter for former President Obama, is working with the group.

As Democrats look to pressure vulnerable Republicans, GOP groups are coming to help their lawmakers too.

The non-profit American Action Network announced a $2 million ad buy across 21 congressional districts to thank Republican lawmakers, including Issa, for their support and provide them with cover in their districts.

Updated May 5 at 10:46 a.m.