On the Constitutionality of Pelosi's delay

Opinion from Professor Cass Sunstein, who likes and otherwise respects McConnell. There is nothing in the Constitution that prevents Pelosi from delaying sending Articles of Impeachment to the Senate. It is appropriate for her to require that the Senate process is fair. There are though Constitutional provisions and Senate Rules for how the impeachment should be handled and McConnell is violating those. Hence he is rigging the process. Sunstein provides measures McConnell could take to at least give the appearance of a fair trial, but Jefferson Smith brings up the valid point that we know we cannot trust that it would be genuine. Should Pelosi then suspend the process indefinitely?