As he looks back at the defeat of former Vice President Kamala Harris last fall, the thing that keeps bothering Andrei Cherny, a onetime Democratic speechwriter and state party leader, is that he didn’t know what Ms. Harris would have done as president if she had won.

The way he saw it, President Trump ran on his own ideas, but Ms. Harris only ran against Mr. Trump’s. “The oldest truism in politics is you can’t beat something with nothing,” Mr. Cherny said.

Now Mr. Cherny, the co-founder of a nearly two-decade-old liberal policy journal, is organizing a group of Democratic thinkers to recreate what Mr. Trump’s allies did when he was voted out of office: draft a ready-made agenda for the next Democratic presidential nominee.

They’re calling it Project 2029.

The title is an unsubtle play on Project 2025, the independently produced right-wing agenda that Mr. Trump spent much of last year’s campaign distancing himself from, and much of his first few months back in power executing.

The fact that Democrats turned Project 2025 into a cudgel against Mr. Trump during the campaign has not deterred Mr. Cherny and the other Democrats working with him from borrowing the tactic. They plan to roll out an agenda over the next two years, in quarterly installments, through Mr. Cherny’s publication, Democracy: A Journal of Ideas. The goal is to turn it into a book — just like Project 2025 — and to rally leading Democratic presidential candidates behind those ideas during the 2028 primary season.