The next stage of President Donald Trump’s impeachment trial will sharpen focus on Chief Justice John G. Roberts Jr.’s role as presiding officer and a looming question: Does he have the power to decide whether the Senate should hear more witnesses and evidence?

A deep dive into the details of Senate rules and impeachment history comes to this conclusion: No, although he might in two less-likely scenarios related to breaking a tie vote.

Ready?

Generally, the Senate’s impeachment rules give Roberts little true power. It sounds important that the chief justice “may rule on all questions of evidence” such as relevancy, materiality and redundancy.

But the rules allow the Senate to vote to overrule him, so a majority of the Senate retains the ultimate power on questions of whether to issue subpoenas for witnesses or documents. Roberts also can decline to rule on a motion either way, and instead ask the senators to vote on it.

So if there is a motion to call witnesses, such as former national security adviser John Bolton, that decision almost certainly would not rise and fall on Roberts. Rather, it would come down to which side has at least 51 senators.

Republicans hold a 53-47 advantage, which is why Democrats have repeatedly said they need four Republicans to join them to get to 51 votes to allow for more witnesses and documents.

“Look, right now our focus is on getting four Republicans. We shouldn’t have to rely on what the chief justice will or will not do,” Senate Minority Leader Charles E. Schumer of New York said Thursday.

But what if only three Republicans vote along with the Democratic caucus on the first big question, whether to allow subpoenas for more witnesses, resulting in a 50-50 tie vote? Things get more interesting and unsettled.

That scenario appears possible, with Republicans Susan Collins of Maine, Lisa Murkowski of Alaska and Mitt Romney of Utah so far expressing an openness to hear from Bolton or other witnesses.

To get this out of the way: Vice President Mike Pence, who can typically break a tie vote in the Senate, does not have a vote or role in impeachment trials, according to Senate Majority Leader Mitch McConnell’s office.

While the Constitution expressly gives the vice president the power to break ties when he presides over other business, it is silent on the question of whether a chief justice can break ties in impeachment trials, said Jeff Blattner, who served as chief counsel to Sen. Edward Kennedy, D-Mass.

McConnell’s office said Thursday that a motion that ends in a tie vote would fail. Keep that in mind for these scenarios. 

If the Senate ties 50-50 on whether to allow motions for subpoenas and witnesses, Roberts could decide not to vote. That would mean the effort would be defeated. 

That scenario seems the most likely, since legal experts who have watched Roberts’ career say he is likely to defer to the Senate and not heavily direct the proceedings. The Constitution gives the Senate the authority to conduct impeachment trials, not the federal courts.

His instincts as chief justice have been to try to keep the Supreme Court from appearing political or stepping into the role of the political branches.

But Democratic senators have voiced support for Roberts to vote to break the tie, appealing to his instinct to not preside over what the public could consider a sham trial.

What if Roberts surprises and decides, as presiding officer, that he could cast a vote to break that Senate tie?

There is a precedent for the chief justice to do so.

In the impeachment trial of President Andrew Johnson, then-Chief Justice Salmon Chase had to rule on motions and issues about live witnesses and more.

Chase sometimes broke ties on a procedural vote. Sen. Charles Sumner of Massachusetts made a motion that one of Chase’s tiebreaking votes was “without authority under the Constitution of the United States,” but the motion failed.

If Roberts follows Chase’s lead, then he could cause the motion to be agreed to, 51-50. Motions on subpoenas for witnesses would be allowed.

In that situation, a senator could call for a vote and a majority could overturn his decision to cast that tiebreaking vote. Subpoena motions would then not be allowed.

But if that vote to overturn Roberts results in another 50-50 tie, then the motion would be rejected because it did not get a majority. Subpoena motions would be allowed.

After that, there are three main scenarios.

Scenario 1: If there is a motion to subpoena Bolton to testify, and Roberts does not rule but instead defers to the Senate, and that results in a 50-50 tie, the motion would be rejected because it did not get a majority. Bolton would not be subpoenaed.

Scenario 2: If Roberts again surprises and decides, as presiding officer, that he could cast a vote to break that Senate tie, then he could cause the motion to be agreed to, 51-50. Bolton would be subpoenaed.

In that situation, a senator could call for a vote and a majority could overturn his decision to cast that tiebreaking vote. Bolton would not be subpoenaed.

But if that vote to overturn Roberts results in a 50-50 tie, then the motion would be rejected because it did not get a majority. Bolton would still be subpoenaed.

Scenario 3: Roberts could surprise and, on that original motion to subpoena Bolton, decide to rule in favor of the motion rather than defer to the Senate. Bolton would be subpoenaed.

In that situation, a senator again could call for a vote to overturn his ruling, and a majority vote could do so. Bolton would not be subpoenaed.

But if that vote to overturn Roberts results in a 50-50 tie, then the motion would be rejected because it did not get a majority. Bolton would still be subpoenaed.

Niels Lesniewski contributed to this report.