Washington (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.

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