As former Vice President Joe Biden prepares to formally launch his 2020 presidential campaign, the central question he faces is whether his consistent leads in all national and most early state polls will withstand the scrutiny of a long presidential campaign. If Rudy Giuliani’s campaign for the 2008 Republican nomination is any precedent, it could be a long time before that question gets answered.

Right now, though Biden is the polling leader, he’s seen by many political observers, including myself, as very vulnerable, and he is not being treated as the clear front-runner. The thinking is that right now, he’s polling well because of high name recognition and he’s still enjoying the wave of popularity among Democrats from being associated with former President Barack Obama and for the gracious way he handled the public grieving after his son’s tragic death. Once he becomes a candidate, the thinking goes, his vulnerabilities will come into focus: his age, his propensity for gaffes, his past stances that seem to be out of touch with the younger and more diverse Democratic electorate. At the same time, voters will be getting to know other candidates better, and his name recognition advantage will erode.