Democratic presidential candidate Beto O'Rourke announced Wednesday that he had signed a pledge against taking campaign contributions from the fossil fuel industry, a move that followed persistent pressure to make the commitment and criticism of his decision not to do so.

In signing the No Fossil Fuel Money Pledge, the former El Paso congressman has promised to not knowingly accept donations of over $200 from PACs and executives of fossil fuel companies. O'Rourke has long rejected PAC money in his campaigns, but as he has become a national figure, he has taken heat for accepting donations from executives, both in his U.S. Senate campaign last year and in the opening weeks of his White House bid.

Announcing his decision to sign the pledge in a video Wednesday evening, O'Rourke also said he would return any contribution over $200 that his presidential campaign has received so far from an executive. "We will not take that money going forward," he added.

The decision is significant. O'Rourke has received questions about the pledge — and why he had not signed it — on a weekly basis on the campaign trail. And when O'Rourke announced a plan to fight climate change Monday, some activists questioned his commitment to the cause given that he had not taken the pledge.

Until now, O'Rourke has dealt with questions about the pledge by emphasizing his desire to run an inclusive campaign that does not write off anyone — including those in the fossil fuel industry.

"If you work in the oil fields, if you answer the phones at the office, if you’re one of my fellow Texans in of our state’s largest employers, I’m not gonna single you out from being unable to participate in our democracy," O'Rourke said last month when confronted about the pledge while campaigning at the College of William & Mary in Williamsburg, Virginia. Pressed by audience members about whether he would take campaign cash specifically from executives, O'Rourke said he was not planning to but still held off on signing the pledge.

O'Rourke cited that episode in the video as he framed his decision to sign the pledge as him being responsive to the young people and activists that he has met on the campaign trail. Those people, he said, "understand that we don't take PAC money ... but given the enormity of our challenge right now [with climate change] ... we don't want there to be any real or perceived conflicts of interest."

O'Rourke's history with the pledge predates his presidential campaign. He signed it while running for U.S. Senate last year but was removed from a list of signees after the race, following reporting that he had taken donations from executives. It appeared O'Rourke's campaign believed at the time that the pledge only applied to PACs.

In any case, O'Rourke's announcement Wednesday marks a major victory for the activists and groups who have sought to make the pledge a litmus test in the Democratic presidential primary. O'Rourke is the 12th candidate to sign the pledge.

A spokesman for one of the groups involved in the pledge, Oil Change U.S., called O'Rourke's decision the "latest indication that the terms of political debate on climate change have fundamentally shifted." The spokesman, David Turnbull, also lauded activists for keeping the pressure on O'Rourke, suggesting he may have never taken the pledge without their persistence.

“While signing the pledge doesn’t prove by itself that any candidate is a true climate leader, it’s a critical indication that they may be willing take on the out-of-control fossil fuel industry that’s threatening our communities and climate every day," Turnbull said. "We absolutely welcome Beto joining 11 other major candidates in signing this pledge to resist the influence of the fossil fuel industry, and look forward to a rigorous debate in the Democratic field moving forward on solutions that match the scale of the problem."