Sen. Tom Harkin caused a fuss on Saturday afternoon by objecting to Rep. Bob Barr's habit of calling senators "jurors." It seems odd that anyone would care one way or the other. But, as William Saletan explains right here, the "juror" word war is really a battle to define the standards for convicting an impeached president. Since no one alive (and almost no one dead) has ever conducted a presidential impeachment trial, many of the larger issues are uncertain. But if they turn on whether the Senate is like an ordinary trial jury, the answer is yes and no. But mainly no.

Talking about the case: DIFFERENT.

In an ordinary trial, jurors may not discuss a case in progress, even with their spouses. Senators observe no such rule. For instance, 19 senators--almost one fifth of the Senate--appeared on political talk shows last Sunday to discuss the impeachment trial with the world.

Talking during the trial: SAME.

In an ordinary trial, jurors do not question witnesses. The idea is that jurors evaluate the narratives presented by defense and prosecution attorneys--jurors aren't responsible for gathering evidence and developing explanatory theories. Senators ordinarily question witnesses during legislative hearings, but during an impeachment trial they assume the juror's passive role.

Conflict of Interest: DIFFERENT.

Individuals with an obvious conflict of interest are excluded from serving as jurors in an ordinary trial. Not so with the Senate. For instance: Sen. Tim Hutchinson's brother (Asa) is one of the House-appointed prosecutors. Sen. Barbara Boxer's daughter is married to Hillary Clinton's brother. Some Democratic senators (e.g. Chuck Schumer) received campaign help from Hillary Clinton. No senator can ignore the effect of any result in this trial on his or her career. In theory, each senator decides whether to recuse him or herself. By the standards of ordinary juries, all 100 should. In real life, not one has done so.

Pre-trial Prejudice: DIFFERENT.

In ordinary trials, jurors are disqualified if they already are familiar with the facts of the case or--if publicity has made that impossible--if they have expressed any opinion about it. Most if not all Senators would be disqualified if that standard applied to an impeachment trial.

Fact Finding: SAME.