Former President Barack Obama congratulated his old buddy Joe Biden for his victory in South Carolina—but reportedly warned him that an endorsement could work against him. CNN reports that Obama called his former vice president on Saturday night. While Obama was reportedly full of praise for Biden’s comprehensive victory in the primary, he said an endorsement won’t be coming any time soon. “We are skeptical that an endorsement coming from us could truly change the political winds right now,” a person close to Obama reportedly told CNN, adding that, if Obama were to endorse Biden, there is “a very real chance it backfires.” Obama still believes his most useful role in the nomination process is as a unifier, with the confidant adding: “If he were try to put his thumb on the scale now, it would take away his ability to do so when it's most needed—the general election ... Weighing in now likely only divides things worse and weakens his standing for when the party will need it most.”