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(CNN) —  

The Democratic Senatorial Campaign Committee has quietly reserved nearly $40 million in air time during the fall campaign in a furious effort to retake the majority and compete with a presidential campaign consuming much of the public’s attention.

The new details provide a window into how Senate Democratic leaders are privately hammering out an election-year strategy to pour big bucks to defend two of their own seats, while aggressively targeting a handful of vulnerable GOP incumbents in order to gain back at least five seats this fall.

According to a source with knowledge of the ad buy, the DSCC is reserving $10 million in air time to target the state’s open Senate seat in Florida, which Sen. Marco Rubio is vacating. The campaign committee is dropping another $10 million in Ohio, in a battle where former Democratic Gov. Ted Strickland is locked in a tight contest with GOP Sen. Rob Portman.

The group plans to bolster the candidacy of Democratic Gov. Maggie Hassan in New Hampshire, with $8 million in the race to unseat GOP Sen. Kelly Ayotte. And the DSCC plans to drop another $5 million to defend two seats – Colorado, where Sen. Michael Bennet is up for re-election, and $4 million in the race for the Nevada seat being vacated by Senate Minority Leader Harry Reid.

The source said that the group is locking down such major buys early in these five states because they are also presidential battlegrounds, so advertising must be reserved early to ensure outside groups get better rates. The source said that air time will be reserved later in other states where there are major Senate races, like Illinois, but unlikely to be contested in a presidential race.

The spending only represents the first wave of advertising this fall, suggesting that the $37 million reserved in these races is just a fraction of what the DSCC will spend in the overall fight for the Senate majority.

A DSCC spokesperson declined to comment.

Democrats have a favorable map this election cycle, with just 10 seats to defend compared to 24 for the Republicans. And with the prospects of Donald Trump or Ted Cruz atop the GOP ticket, many Democrats believe that swing voters in purple states will end up voting for their candidates down-the-ticket and help them take back the Senate.

Yet, Democrats have their own challenges as well, including a lack of enthusiasm among progressives for their party’s presidential front-runner, Hillary Clinton.

Moreover, the infighting between the party’s base and establishment is playing out in down-ticket Senate races, mirroring the increasingly tense battle between Clinton and Sen. Bernie Sanders on the presidential level.

In Florida, the candidate preferred by the party establishment, Rep. Patrick Murphy, is facing off against an unpredictable progressive firebrand, Rep. Alan Grayson, in the August primary.

In Pennsylvania, the DSCC’s choice, Katie McGinty, has benefited from $1.1 million in advertising by the committee ahead of the contested April 26 primary. But former Rep. Joe Sestak is the heavy favorite to win the Pennsylvania Democratic primary, something that has prompted fears among many in the party establishment about his viability against GOP Sen. Pat Toomey this fall.