The likely impeachment of Donald Trump will be the third presidential impeachment trial in our country’s history. The first two were Presidents Andrew Johnson in 1868 and Bill Clinton in 1999.

Impeachment in the House needs only a majority vote, while conviction in the Senate requires two-thirds “of the Members present.” Assuming all 100 senators show up, and all 45 Democrats and the two independents vote to convict, it will still still take 20 Republican votes.

You can never predict how a jury will come out, and I make no predictions here. I will simply speculate on some of the issues Chief Justice Roberts will likely face as the presiding jurist.

The Constitution isn’t very helpful. Article I tells us is that the chief justice shall preside, but otherwise the Founding Fathers left it up to the Senate to figure out how to proceed.

During his 2005 confirmation hearing, Roberts said, “I will remember that it’s my job to call balls and strikes and not to pitch or bat.” Little did he imagine he would be sitting as a trial judge looking out at 100 senators, many of whom will have made up their minds before hearing the evidence. It’s almost like starting the game in the ninth inning.

Trump’s lawyers will likely move to dismiss the case, raising procedural objections and arguing that the impeachment charges do not rise to the level of “high crimes and misdemeanors.” If such a motion were to succeed, which is highly unlikely, it would effectively “unimpeach” the president.

Could the Senate overrule a decision by Roberts? History provides no answer, but during the Clinton trial, Chief Justice Rehnquist declared, “The Senate is not simply a jury. It is a court in this case.”

The Constitution gives the Senate the power to hold a trial, but doesn’t say it has to do so. “Constitutional hardball” sounds pretty radical, but when Chief Justice Salmon P. Chase (who lived in Keene during his boyhood) made rulings during the Johnson impeachment trial, the Senate overruled him more than once.

Mitch McConnell has said the Senate rules require a trial, but he could change his mind and let senators vote whether to go forward or go home. If you’re McConnell and just want the whole thing to go away, it might be simpler to “Garland” the proceedings and “let the voters decide.”

The Senate rules require the Senate to “receive” the House managers for the purpose of “exhibiting” the articles of impeachment. The sergeant at arms then gives the equivalent of an “Oyez, oyez,” and the the trial goes forward, every day except Sundays.

Will President Trump be there? When the Johnson impeachment trial began, Chief Justice Chase called his name three times, but he was nowhere to be seen. His lawyer, former Supreme Court Justice Benjamin Curtis, appeared for him. I expect President Trump will follow Johnson’s example and be elsewhere.

Once the trial starts, senators are required to “keep silence, on pain of imprisonment.” I suppose the Senate could change its rules to allow direct questioning, as occurred in the impeachment trial of New Hampshire Chief Justice David Brock in 2000, leaving it to the chief justice make calls far afield from his usual umpire duties.

Once the testimony gets underway, Roberts will have to decide whether to allow hearsay, opinion or other evidence usually considered inadmissible. I think he should enlarge the strike zone and take a broader approach based on whether he considers the evidence reliable.

In the ordinary case, the judge explains the burden of proof to the jury: “preponderance of the evidence” in most civil cases; “beyond a reasonable doubt” in criminal trials. President Clinton lost his argument in favor of the criminal standard. The Senate decided not to adopt any particular standard, leaving it up to each senator’s conscience, as did the New Hampshire Senate in 2000.

I haven’t even gotten to the question of just what offenses constitute impeachable “high crimes and misdemeanors.” Alexander Hamilton described impeachment as “a method of national inquest into the conduct of public men” accused of violating the “public trust.” Then-Congressman Gerald Ford once said, “An impeachable offense is whatever a majority of the House of Representatives considers it to be at a given moment in history.”

Justice Potter Stewart didn’t need to define “obscenity” because “I know it when I see it.” The same is true here, and the senators will define the words for themselves.

Joseph D. Steinfield is a lawyer who lives in Keene and Jaffrey. He can be reached at jsteinfield@princelobel.com.