Calling climate change “an existential threat,” Joe Biden, the front-runner in the Democratic presidential race, proposed achieving 100% clean energy and net-zero carbon emissions by 2050 as part of a $5 trillion climate plan that would be paid for by undoing President Donald Trump’s signature tax cuts.

Biden pledged to go “well beyond” the climate policies embraced by the Barack Obama administration with a series of executive orders starting on his first day in office, and said he’ll demand that Congress enact legislation enforcing his mid-century emissions reduction goal, according to Bloomberg. “We must take drastic action now to address the climate disaster facing the nation and our world,” Biden said.

The 22-page plan comes as climate change has emerged as a litmus test for Democrats in the 2020 campaign. Candidates have been racing to out-do each other with calls for carbon taxes, fossil fuel bans, and multi-trillion dollar climate change proposals.

Biden, Obama’s vice president and a centrist running on rebuilding the middle class, has already received criticism from rivals and environmental groups for not being strong enough on the issue, even before the release of his climate proposal.