The Senate rules for impeachment trials have remained largely intact since the proceedings to oust President Andrew Johnson in 1868. While a majority of the Senate can change the rules at any time, political considerations will mitigate against anything but minor tinkering for the trial of President Donald J. Trump. Public polling has indicated that a majority of Americans believe the recent House proceedings were conducted fairly. And for the Senate to stray too far from past protocol, many believe, would not be a good look.

Furthermore, substantive rule changes would increase the political pressure on the few politically vulnerable Senate Republicans, such as Susan Collins of Maine, or Corey Gardner of Colorado. Shifts in procedure might unnecessarily test the loyalty of senators like Utah’s Mitt Romney and Alaska’s Lisa Murkowski, whose brands allow them to be independent of Trump. But even assuming the Senate follows the rules that were largely in place for the Johnson, Nixon, and Clinton matters, whatever transpires is going to be quick and calculated to produce few moments of memorable political theater.

This raises the question: once the House and the Senate end their current squabble, and Nancy Pelosi hands the articles of impeachment off to the upper chamber, who will preside at the Senate trial? Under the Constitution, that role goes not to the Senator majority leader, Mitch McConnell, but to Chief Justice John Roberts. In certain Democratic circles there is a shared fantasy that Roberts, who has occasionally emerged as an independent voice, a figure above today’s tribal politics, will, unlike the Republican senators, refuse to toady to Trump. This, alas, is highly unlikely to come true. That is because Roberts, even as chief justice of the United States, will not exert powers remotely comparable to those wielded by a judge in the usual federal criminal trial.

The saying that a judge is the king of his courtroom is in many senses true. Under the Anglo-American tradition, a judge is standing in for the monarch, who was once the sole source of law. But most of the powers that a federal judge typically exerts—to decide who may be called to testify, to control the schedule of the proceedings, to rule on the admissibility of evidence, to say yea or nay about virtually any question asked—belong explicitly to the Senate in an impeachment trial.

The Senate rules are plain: “The Senate shall have power to compel the attendance of witnesses, to enforce obedience to its orders...to punish in a summary way contempts...and to make all lawful orders, rules, and regulations which it may deem essential or conducive to the ends of justice.”

The chief justice has the power to rule on objections to evidence, saying for example, that certain testimony is irrelevant—but even that power is limited. A majority of the Senate can overrule the chief justice, and any single senator has the power to demand that a vote be taken on any given ruling by the chief. For that reason, Roberts is likely to be, much as his mentor Chief Justice William Rehnquist was during the Clinton impeachment, little more than a ceremonial presence, deciding little of substance.

The contrast between a typical criminal trial and what will go on in the Senate can best be understood by considering the matter of subpoenas. Under the Federal Rules of Criminal and Civil Procedure, in a normal trial any party may issue a subpoena in the name of the court, requiring the production of testimony or documents. Witnesses who believe the subpoena is invalid for some reason can then petition the trial judge not to enforce it.