Obama intervened often in START negotiations

 “Dmitry, we agreed,” advisers quoted a frustrated President Obama saying in a February phone call with Russian President Medvedev about the latter's stance on missile defense. “We can’t do this. If it means we’re going to walk away from this treaty and not get it done, so be it. But we’re not going to go down this path."  Sources close to the negotiations agreed that the process had been much harder than anticipated, and that the President played an active role.  “He has been personally involved in this in a way I don’t think other presidents have been,” said White House Chief of Staff Rahm Emanuel

The agreement was completed just weeks before the upcoming Nuclear Security Summit in Washington.  “The larger meaning [of the treaty] is the delegitimization of nuclear weapons,” Partnership for Global Security head Kenneth Luongo told the New York Times. “Obama will be able to go [to upcoming nuclear security meetings], and Medvedev as well, and say, ‘Here’s what we did on disarmament. Now we need to get serious about nuclear terrorism and nuclear materials.’ ” 
Global Security Newswire