House Majority PAC, the Democratic super PAC allied with Representative Hakeem Jeffries of New York, the House minority leader, said on Sunday that it would spend $186 million on television and digital advertisements for this year’s elections — the largest early investment in the group’s history.

The hefty expenditure will cover 58 media markets in 45 districts, targeting Republican seats in districts that President Biden carried in 2020 as well as Democratic seats in districts that former President Donald J. Trump won. As part of that spending plan, $40 million will go toward digital advertisements, the group said on Sunday. Details of the ad buy were first shared with CNN.

In an interview on Sunday, the House Majority PAC president, Mike Smith, described the group’s plan for this election year as “an offensive strategy.” Democrats need to win just four seats to clinch a House majority, and they have said that doing so depends on races in New York and California. The group is spending the most in those states to unseat vulnerable Republican freshmen and to maintain the ample — and costly — messaging needed to break through to voters.

“The significant investment is the seriousness of which we are taking this election,” Mr. Smith said. “The core districts that are going to make or break whether or not Democrats win or lose the majority this fall are kind of consolidated, and a lot of them take place in the most expensive media markets in the country.”

Mr. Smith also noted that the group had invested early in advertisements in states like Ohio, Montana and Michigan, where there are a handful of competitive U.S. Senate races and tight margins for the presidential race. It is particularly focused on appealing to voters in districts with substantial Black, Hispanic or Asian American populations, in addition to swing districts.

Cash-flush Democrats are doling out hefty sums to protect vulnerable candidates ahead of a tough election in November. Atop the ticket, President Biden and his allies have out-raised Republicans so far: The president’s re-election campaign said it had $192 million on hand, a sum that includes funds raised by the national party and allied groups. As Mr. Trump fought to close the fund-raising gap, his campaign boasted of a $50 million haul from a high-dollar fund-raiser he hosted on Saturday in Palm Beach, Fla. ​

But Democrats have not shied away from the need for candidates farther down the ballot to outperform Mr. Biden, whose sagging approval ratings could present a drag. Asked if such a large, early investment was a reflection of the perceived challenges that Democrats will face sharing a ticket with the president, Mr. Smith said that the investment was not a response to presidential polling.

“It has less of a reflection on anything other than the fact that we need four seats to win,” Mr. Smith said. “We’re not taking anything for granted and we’re making the investments known now, across the battlefield.”

The advertisements will largely focus on reproductive rights, the economy and perceived Republican “extremism” that has hampered progress in Washington. The advertisements will start running on Monday. The number of markets and how much the group will spend may vary from initial placement as the campaigns continue and groups reassess their priorities.