The Constitution states that in impeachments to get presidents, the chief justice of the Supreme Court is the presiding officer. For lesser impeachments, the presiding officer has become the same as for other Senate company -- possibly the president or a senator. The Constitution isn't clear on who must preside over impeachments for former presidents.
If Roberts does not preside over a Senate trial, Harris would likely have the option of whether to preside herself. The transition organization for the incoming Biden administration did not respond to your request for comment asking whether Harris would do that.
If Harris passes on presiding over the trial, it would fall into a senator, likely Sen. Patrick Leahy, D-Vt., who's the longest-serving Democrat.
Roberts, whose occupation makes him the de facto caretaker of the national judiciary, is seen as an institutionalist who aims to maintain the Supreme Court out of highly controversial political waters. He's famous for frequently sidestepping sweeping decisions on important problems and crafting narrow opinions to distribute with the case at hand while a number of his colleagues beg the court to make broader decrees.
Throughout the 2020 Trump impeachment, Roberts failed for a tie-breaking vote in the Senate when asked by Senate Minority Leader Chuck Schumer, D-N.Y.
"I have a parliamentary inquiry," Schumer said.
Roberts reported that the votes Chase broke ties were minor procedural motions, and noted that the votes were odd in the history of impeachments and happened a century and a half ago.
"If the people of this body, elected by the people and accountable to them, divide equally on a motion -- the rule is that the movement fails," Roberts stated. "I think it would be improper for me personally, an unelected officer from another branch of government, to maintain the power to change that outcome so the motion would triumph."
Roberts at another stage in the impeachment trial was visibly irked when Sen. Elizabeth Warren, D-Mass., asked a question regarding the legitimacy of the Supreme Court.
Schumer was likely referring to the possibility that Roberts could decide the fate of a movement to hear witnesses in the 2020 Trump impeachment trial, which eventually failed 51-49.
The Supreme Court's public information office did not immediately respond to a petition to confirm whether Roberts would preside over a Senate trial, or whether he considers the Constitution mandates that he oversee the impeachment trial of a former president.