The top Senate Democratic super PAC plans to spend about $80 million to reserve fall airtime for television commercials in nine battleground states, a sizable early investment in pursuit of winning control of the Senate.

Senate Majority PAC will soon secure post-Labor Day airtime in Arizona, Florida, Indiana, Missouri, Montana, Nevada, North Dakota, Tennessee and West Virginia, the group told The Washington Post. The spending represents its first wave of fall reservations, officials said.

“We are implementing an aggressive media strategy,” said Senate Majority PAC President J.B. Poersch, a close ally of Senate Minority Leader Charles E. Schumer (D-N.Y.). “We look forward to building off our existing momentum with smart, tactical planning to ensure victory in November,” he added in his statement.

Senate Majority PAC declined to detail how much money it intends to spend in each state. A strategist with the group said every state has at least a seven-figure ad buy.

Democrats are mostly on defense in Senate races this year, with 26 of their seats up compared to just nine for Republicans. Ten of the Democratic-held seats are in states President Trump won in 2016.

Republicans hold a 51-49 Senate majority. While President Trump’s unpopularity and historical trends in a president’s first midterm spell trouble for the GOP, party strategists feel better about the playing field in the Senate than they do in the House. Trump is popular in key states likely to decide control of the Senate.

With its reservations, Senate Majority PAC is mostly trying to protect vulnerable Democratic senators in states Trump won by a wide margin: Indiana, Missouri, Montana, North Dakota and West Virginia. It is also trying to fortify Florida, where Trump won a close race and Democratic Sen. Bill Nelson faces a challenging reelection bid against Republican Gov. Rick Scott.

Democrats see Nevada, the only state won by Hillary Clinton where a Republican senator is seeking reelection, as their best chance to flip a GOP-held  seat. Open seat races in Arizona and Tennessee represent their next best chances.

Notably absent from the group’s initial investment are Ohio and Wisconsin, two states key to Trump’s win that Democrats are defending this year. Strategists in both parties believe that the Republican chances of capturing those seats is not as strong as it is in others.

Also missing from the list is Mississippi, where a November special election for a GOP-held seat has been on Democrats’ radar. If no candidate wins a majority there on Election Day, the top two finishers will advance to a runoff.

The nine states in which Senate Majority PAC is investing are the same nine that Senate Majority Leader Mitch McConnell (R-Ky.) said would likely decide the battle for the Senate majority in a recent interview with The Washington Post.

Schumer said in a recent interview with The Post that the number of Democratic seats up for grabs has narrowed to four. He declined to identify them.

Democrats working to win the majority have concluded that the four most worrisome states they have to defend are Florida, Indiana, Missouri and North Dakota.

The Senate Majority PAC investments are subject to changes, the group said. It is common for organizations to pull back or add more money as Election Day nears and races become more or less winnable. Senate Majority PAC may also spend money in other contests.

As a super PAC, Senate Majority PAC can raise unlimited money but cannot coordinate strategy with each campaign.