In just 15 months, NextGen Climate Action has grown into one of the mightiest spenders of the midterm election.  And with the latest round of pocket money from founder Tom Steyer, it now has $19 million to spend within two weeks of the November 4 election.

With his latest gift, Steyer’s contribution to NextGen Climate now exceeds the $50 million he had promised to spend at the outset. He gave $16 million on October 14 — the super PAC’s largest contribution received to date — meaning that NextGen has now racked up close to $58 million from the California hedge fund billionaire. Steyer previously made $15 million donations in September and August. As of last month, Steyer already topped our ranking of donors of disclosed cash.

Hedge fund magnate Tom Steyer gave $16 million to NextGen Climate Action, the latest installment of his regular cash flow to the super PAC he created. (Flickr/Fortune Live Media)

Though NextGen Climate has not succeeded in raising the matching $50 million Steyer had envisioned, it’s also rounded up some solid contributions from various other well-heeled donors. In the first two weeks of October, television executive Marcy Carsey, who produced “That 70′s Show” and “The Cosby Show”, gave $300,000 to the super PAC. Last month, Samuel “Rob” Walton, the son of Wal-Mart founder Sam Walton, gave $200,000 and hedge fund magnate Meridee A. Moore gave $1 million. Pat Stryker, the heiress whose cash helped turn the Colorado legislature blue, also gave $500,000 in September.

NextGen Climate Action is honing in on several battleground states that might determine who controls the Senate. It’s already spent $6.5 million in Colorado, $3.7 million in Iowa and $3.2 million in New Hampshire.

Update: This post was updated to correctly state how long the super PAC’s has existed, which was previously listed as eight months.