We don’t know exactly what will happen when President Biden and former president Donald J. Trump take the debate stage in Atlanta tonight. We do know, however, that the first debate between the major party candidates is happening earlier in the election season than usual. And we also know that we’ve seen a version of this show before. Their past matchups have featured bitter insults, constant interruptions and were political spectacles judged more on optics than on substance. This year, considering that the candidates are offering radically different visions for the country, it’s hard to imagine an election in which the substance would matter more. So, today, at least on “The Run-Up,” there’s no buzzer, no microphone muting and no debate-stage theatrics. Instead, we call four Times colleagues to talk about what the candidates are actually promising for a second term on four key issues: the economy, immigration, abortion and foreign policy.