About 72 percent of Californians eligible to vote have registered to cast their ballots in Tuesday's presidential primary, marking a record number for the state, according to Secretary of State Alex Padilla.“In the 45 days leading up to the voter registration deadline, there was a huge surge in voter registration — total statewide voter registration increased by nearly 650,000," Padilla said in a statement, reports. "Part of this surge was fueled through social media, as Facebook sent a reminder to all California users to register to vote.”On Friday, Padilla's office released a report showing that just more than 17.9 million voters were registered as of the state's May 23 deadline, marking the most registered voters the state has ever had heading into a primary election.About 45 percent of the state's voters registered as Democrats; 27 percent registered as Republicans, and unaffiliated voters make up another 23 percent.According to the report, there were about 17.2 million registered voters heading into the 2012 presidential primary.Hillary Clinton and Bernie Sanders are fighting almost neck-and-neck for control of California for a prize that won't likely deliver Sanders the delegates he needs to clinch the Democratic nomination, but would bolster his refusal to leave the race before the party's convention in Philadelphia.Meanwhile, presumptive GOP nominee Donald Trump has no competition in California, but has been holding a series of rallies in hopes of winning support in the traditionally liberal-leaning state this fall.