The Democratic National Committee announced on Tuesday that it would pour $15 million into the party’s ground game in seven battleground states, an early cash infusion into the nuts and bolts of campaigning as Republicans hold their national convention in Milwaukee.

The money, which will go directly to the Democrats’ state parties, will be used to open more field offices, expand data collection efforts and hire staff members to cover more terrain in Arizona, Georgia, Michigan, Nevada, North Carolina, Pennsylvania and Wisconsin.

“This is the largest-ever investment made to battleground state parties at this point in time,” Jaime Harrison, the chair of the D.N.C., said in a statement. “And we continue to build our state-by-state war chests in preparation to re-elect President Biden and Vice President Harris in November.”

The $15 million summer expenditure amounts to a bet by Democrats that a sophisticated and sprawling ground game in battleground states can overcome the turmoil engulfing President Biden’s campaign, after weeks in which key elected Democrats and donors have defected from him and called for him to step aside over concerns about his age and acuity.

And in the new era of widespread early voting, which Democratic voters have used more frequently than Republican ones, early field investments in state parties can be crucial to getting out the vote. Political ground games are no longer tailored for only the final week of October and early November, but instead a much longer stretch in which voters are casting ballots early and by mail.

“This election was always going to be close, and regardless of Beltway media narratives, the entire election is going to come down to operation and turnout in the battleground states,” Mr. Harrison said.