Number of mass-shootings they will collectively prevent: Zero.
Via NBC News:
Colorado Gov. John Hickenlooper signed landmark new gun laws on Wednesday expanding background checks on gun purchases and limiting the size of ammunition magazines, placing the traditionally firearm-friendly state among the handful to pass new restrictions in the wake of the shooting in Newtown, Conn.
Eric Brown, a spokesperson for the governor, confirmed that Hickenlooper had signed the bills in an email to NBC News.
Vice President Joe Biden personally lobbied lawmakers to get enough votes to get the bills through the Democrat-controlled House of Representatives in February. The measures backed by state Democrats cleared the state Senate on March 12.