NPR.org's Sen. Patrick Leahy To Preside Over Trump's Senate Impeachment Trial says:
Chief Justice John Roberts presided over Trump's first impeachment trial, but now that Trump is a former president, Roberts is not constitutionally obligated to preside.
The Constitution says, "When the President of the United States is tried, the Chief Justice shall preside." And Roberts did that when Trump was tried last year. This time, however, the chief justice let it be known he did not want to preside now that Trump is no longer president. On Monday, a Supreme Court spokeswoman said Roberts would have no comment.
It is unclear whether Senate leaders ever consulted Roberts. More likely, Roberts, who has tried mightily to keep the Supreme Court out of politics, headed them off at the pass and made his views clear.
Question: How exactly did Justice Roberts "let it be known", "head them off at the pass" and "make his views clear" that he did not wish to preside over the 2nd presidential impeachment of forty-five? Was it really a question of preference or one of law?