The true measure of President Biden’s climate ambition may be the clean electricity standard he tucked into his massive $2.2 trillion infrastructure spending plan. Its goal is striking: 80% clean power in the United States by 2030.

The details, however, are vague. And so is Biden’s plan B if it fails—an uncertainty that’s worrisome to both activists and academics. The lack of a clear backup plan underscores the importance of passing a clean electricity standard, they say.

If the clean electricity standard doesn’t survive Congress, it will put pressure on the need to drive climate policy through targeted spending, said John Larsen, a power system analyst with the Rhodium Group, an economic consulting firm.

“I don’t think the game is lost at all if a clean electricity standard doesn’t get through in this round,” Larsen said. “But there’s a difference between not passing a clean electricity standard and passing the right spending package.”

In his few months in office, Biden has outlined plans to bring the United States back into the international Paris climate accord, pause oil and gas leasing on public lands, boost the electric vehicle market, and target clean energy investments in vulnerable communities most affected by climate change.

But those are largely executive orders and spending proposals—and unlikely to last beyond his administration if the next president favors fossil fuel usage over climate policy. The clean electricity standard, which would decarbonize 80% of the electrical grid by 2030, is different.