You may have seen this link pop up in your Facebook feed over the weekend:

Tens of thousands have joined a new campaign, called Swing Left, that aims to help Democrats win the majority in the House of Representatives in 2018. More than 100,000 people have signed up since Inauguration Day, according to Swing Left’s founders.

The website maps 52 swing districts – defined as areas where the incumbent won by 15% of the vote or less – and helps Democrats find the swing district located closest to their home.

People who sign up for Swing Left receive weekly emails about how to fundraise and volunteer for Democratic candidates. For them to win the House majority, Democrats would need to take 80% of all those swing districts in the next election, which means flipping 24 districts that elected Republican representatives in 2016.

Swing Left is a grassroots effort – started by individuals from a variety of industries including tech, media, nonprofits, and art – that aims to seize on mounting opposition to Trump’s administration. The day after Trump was sworn in, an estimated 500,000 people convened for the Women’s March on Washington, while millions more participated in sister marches across 60 countries. Swing Left’s site has been shared about 217,000 times on Facebook, according to analytics from ShareCount. And more than 68,000 people have also signed up to receive a Facebook reminder about Congress’ 2018 election.

“We’re starting early to unify progressives who promote tolerance, equality, unity, and fairness,” Swing Left’s site says. “To out-organize Republicans, we can’t wait.”