Now Democrats are reliving the political frustration from the Obama years. Right when the Democrats are in desperate need of strong leadership, looking for someone who has the muscle and clout to push back against the aggressive, smash-mouth, destructive politics of Trump, the former president has not done nearly enough to step in to fill this void. After an interval, Bill Clinton brought a fierce sense of urgency to the campaign trail in his post-presidency, and Jimmy Carter has done the same with regards to foreign policy. While Trump has provoked an extensive grassroots counter-mobilization, as Theda Skocpol and Lara Putnam document in the new issue of Democracyit’s largely leaderless.When Obama became president in 2009, Republicans could afford to have former President George W. Bush sit on the sidelines as they rebuilt their strength. Unlike Obama, Bush was hugely unpopular. But more importantly, the right had its institutions as a solid base for revival. The grassroots energy of the Tea Party was connected to these entrenched institutions, from Fox News to Dick Army’s FreedomWorks. But the Democratic Party can’t afford to wait; it needs Obama to learn from one of the great mistakes of his own presidency: his failure to take seriously enough the grave political threat his party was facing.Some Democrats fear that Obama reentering the picture would energize conservatives and move the party backwards in time—rather than encouraging new leaders to emerge with an eye toward 2020. But conservatives are energized, organized, and mobilized regardless of which Democrat stands in the public spotlight. This cautious logic replicates the same mistake that Obama made when he backed away as president from several tough fights with the GOP hoping his restraint would tone things down. It didn’t. And Obama can help promote new Democratic voices.

Indeed, Obama came to the forefront in 2004—when former President Bill Clinton was out on the hustings campaigning, and Obama was given a spot on the stage at the convention that nominated Senator John Kerry. Given that Obama ended his term with high approval ratings and remains an admired figure within much of the electorate, he could use his standing to build support to check Trump, the most unpopular president in recent history. A vibrant party is capable of handling many voices, new and old, at the same time. Frail and depleted parties are the ones that can’t walk and chew gum at the same time.

The last time Obama was too timid, the Republicans roared. His party can’t afford to see Obama make that same mistake once again.