The Senate Democrats' top super PAC is ramping up its effort to flip Republican-held Senate seats, announcing another $54 million in television advertising across four key battleground states heading into the final stretch of the midterm election campaign.

According to Axios, the latest ad buy from Senate Majority PAC (SMP), which is aligned with Senate Minority Leader Chuck Schumer, underscores where Democrats believe they have their best opportunities to erode the GOP majority.

The largest investment is reportedly headed to Ohio, where the group is adding $24 million in support of former Sen. Sherrod Brown, increasing its total reservation in the state to $60 million.

Iowa will receive an additional $17 million backing state Sen. Josh Turek, bringing the group's total commitment there to $30.5 million. In North Carolina, SMP is adding $11 million for former Gov. Roy Cooper, raising its reservation to $42.5 million.

The group is also putting another $2 million behind former Rep. Mary Peltola in Alaska, boosting its total spending in the race to $11 million.

"Injecting new resources into the four most competitive Senate races shows just how clearly the battleground map has shifted toward Democrats," Senate Majority PAC spokesperson Lauren French told Axios.

The latest spending comes as Republicans continue working to defend their Senate majority. Axios reported that the GOP's most recent major advertising reservations were focused largely on protecting incumbent senators and reinforcing the party's electoral "red wall."

Even with the new Democrat investment, Republicans maintain a significant financial edge.

According to Axios, the Senate Leadership Fund (SLF), the super PAC aligned with Senate Majority Leader John Thune, reported $238 million in cash on hand at the end of June, compared with $126 million for Senate Majority PAC.

The Democrat group indicated Wednesday's announcement is not expected to be its final advertising push before Election Day. Axios reported that SMP plans to make additional television reservations in the coming months but has not revealed its digital advertising strategy.

Republicans have already outlined an aggressive campaign plan of their own. In April, Senate Leadership Fund announced it intends to spend $342 million during the election cycle across television, digital advertising, and get-out-the-vote efforts, according to Axios.

The competing spending plans highlight the high stakes of the battle for Senate control, with both parties preparing to flood the nation's most competitive races with advertising in the months ahead.