Ms. McGowan said that for months her group had been raising the alarm about Mr. Trump’s early online spending advantage.

“It started to feel as though we were really screaming into the abyss,” she said. So they decided to take matters into their own hands.

Ms. McGowan said the group had already raised approximately 40 percent of the planned $75 million budget. Mr. Plouffe has joined as both a political adviser and to help raise funds. The spending will be made across two groups, Acronym, which is a nonprofit that does not disclose its donors, and Pacronym, a political action committee, which does. (The group’s winking moniker is a poke at the frequent practice of settling on a meaningful series of words to form an acronym for a nonprofit; they have skipped that alphabet-soup step entirely.)

“We’re absolutely, as a party, not doing enough and I don’t know that $75 million is enough,” Ms. McGowan said. “We can’t afford to not do this work right now.” Of the fact that some of her group’s donors would remain undisclosed, she said, “We have to play on the field that exists,” noting that Mr. Trump is aided by such funds, as well.

Mr. Trump is not just spending heavily on advertising — he has dozens of Facebook ads currently running that cite the “baseless attacks” from Democrats on impeachment — he is also benefiting from a conservative media echo chamber that amplifies his message and a meme factory of MAGA (“Make America Great Again”) supporters cranking out content in hopes of a presidential retweet.

Much of Mr. Trump’s advertising budget has gone toward recruiting new donors. His campaign manager, Brad Parscale, announced Friday that the Trump campaign had raised $19 million online in October.

Mr. Plouffe said he knew the advantages of incumbency intimately from the 2012 Obama re-election campaign and wanted to blunt the current White House’s advantage.