New York City Mayor Michael Bloomberg has spent at least $14 million in support of new gun control legislation since December, when the Obama administration began its push for gun control in the wake of Adam Lanza's shooting spree in Newtown, Conn.

Bloomberg's group had supported calls for a so-called assault weapons ban, limits on magazines, and expanded background checks. The assault weapons ban and magazine limit were unlikely to gain traction, but Democrats had hoped the background check would find a more receptive hearing on Capitol Hill. However, this afternoon the Manchin-Toomey amendment to implement background checks for gun purchases failed by a vote of 54-46. Bloomberg announced a $12 million ad campaign in March that aimed to persuade senators in 13 states to support an eventual gun control bill.

One of the Democrats targeted by Bloomberg, Sen. Mark Pryor (D., Ark.), voted no on the amendment despite Bloomberg’s ad campaign. Others, like Sen. Jeff Flake (R., Ariz.), were unfazed by the onslaught of Bloomberg-funded attack ads.

Bloomberg’s Super PAC Independence USA spent nearly $2.3 million in January and February in addition to the massive ad campaign. The majority of this money was spent to defeat former Democratic Rep. Debbie Halvorson in an Illinois special election.