Before I tried my first federal case, my supervising attorney gave me three invaluable pieces of advice: Never forget who your audience is. You have 12 seconds to get their attention. Grab them by the throat.

The seven impeachment managers selected by House Speaker Nancy Pelosi (D-Calif.) will begin to prosecute the case against President Trump on Tuesday. They would do well to keep that advice in mind.

In this instance, though, the jury is not the audience. Trump is unique among criminal defendants: The United States senators who will sit in judgment have long since made up their minds. Lindsey Graham (R-S.C.) put it bluntly: “I’m not trying to pretend to be a fair juror here.” So did Majority Leader Mitch McConnell (R-Ky.): “The way that impeachment stops is a Senate majority with me as majority leader.” Presidential hopeful Elizabeth Warren (D-Mass.) has been just as unequivocal: “This is a man who has broken the law, and he should be impeached.” And so has her Democratic presidential rival Bernie Sanders (I-Vt.): “The House of Representatives rightly carried out its constitutional responsibility by voting to impeach Donald Trump, the most corrupt president in our history.”

The process is so hyper-partisan that, almost without exception, a member of either party crossing the aisle to convict or acquit will be catapulted out of Congress. To convict and remove the president from office requires a two-thirds majority in a 100-member body where the Republicans hold 53 seats. It’s not going to happen.

No, the throats to be grabbed are those of the American public — specifically, the small but crucial number of people who live in swing states and have yet to make up their minds. House managers must convince this skeptical sliver that Trump committed high crimes and misdemeanors by using the power of his office to try to dig up dirt on his political rival, former vice president Joe Biden, and his son Hunter Biden, and then obstruct legitimate efforts by Congress to investigate his wrongdoing.

If they succeed, they will achieve a public nullification of the Senate’s foregone verdict, in the form of Trump’s defeat in the November elections.

So how best to use that crucial first 12 seconds?

Human beings are highly distractible and easily bored. Smartphones and social media await. If you don’t get their attention immediately, you are unlikely to get it at all. Normally, prosecutors would lead off with a cogent, compelling summary of coming attractions in the form of expected testimony and documents: You will hear John Bolton describe the “drug deal” cooked up at the behest of the president! You will see the Lev Parnas to-do list that says “Get Zelensky to Announce that the Biden case will Be Investigated”! But it isn’t clear that McConnell will allow the House managers to call witnesses or present documents at all.

To secure America’s attention, House managers should tantalize, previewing the case as a binge-worthy whodunit and casting McConnell as a meanie preventing the public from seeing it. That entails making the 12-second argument that without witnesses and evidence — particularly firsthand, as-yet-unheard-from witnesses and the trove of documents released Tuesday — there will be no real-time “reveal,” with its promised resolution to the world’s most-watched criminal investigation. The late-breaking decision by Bolton, the former national security adviser, to offer to cooperate, and the 11th-hour disclosure of evidence provided by Parnas, a close associate of Trump’s personal lawyer Rudolph Giuliani, documenting a pressure campaign to get Ukrainian President Volodymyr Zelensky to announce a Biden investigation, give prosecutors plenty of material to work with.

“Let the process play out!” is a message that will resonate with many independent and centrist voters — even 40 percent of Republicans agree that witnesses should testify. Americans’ outrage at being deprived of the chance to see and hear for themselves could foster the perception that Republicans can’t handle the truth, and could push the handful of Republican senators who hew to the center to demand that McConnell relent.

Such a victory would be Pyrrhic and transformational at the same time. Pyrrhic because the chances that it would change the outcome are slim. Transformational because live witness testimony would create a momentum of its own. Trials are inherently fluid and unpredictable. Live testimony would turn a D.O.A. dud into must-watch TV complete with a flame-throwing defense team, witnesses potentially bearing bombshells, and Chief Justice John Roberts as referee. What House managers want is the attention of the tens of thousands of viewers who live in swing states and will cast votes in November. That’s the way to get it.

They are the only audience that matters. No amount of admonishment to be fair will change the fact that the 100 senators tasked with sitting in judgment bear little resemblance to a typical jury composed of 12 random people who know nothing about the case and have no stake in the outcome. The real jurors will render their verdict at the ballot box: They are the true-crime-loving American people who would like nothing better than ringside seats at the Trial of the Century. They want heroes and villains, they want twists and turns, and they want the satisfaction of believing that they got to be a part of uncovering the truth.

House managers need to deliver by pressing their case in the form of viral moments (like Bolton testifying under oath that yes, he told his deputy that Giuliani was a lowlife criminal with outsize ambitions) and acerbic asides pithy enough to generate memes (perhaps a picture of all the president’s men — Attorney General William P. Barr, Vice President Pence, the ever-acting White House chief of staff Mick Mulvaney, and Giuliani and his henchmen Parnas and Igor Fruman — spilling out of a car in matching clown suits).

But a good offense isn’t enough. If they want to prevail, the House managers have to anticipate and blunt vociferous efforts by the president’s defense team to wrest control of the story. This team will now include former O.J. Simpson “Dream Team” member Alan Dershowitz; Kenneth W. Starr, the former independent counsel whose investigation of President Bill Clinton led to his impeachment; Trump’s personal attorney Jay Sekulow; and White House Counsel Pat Cipollone. By calling witnesses of its own, including the Bidens, the president’s team could distort the prosecutors’ narrative and turn the proceedings into a circus.

Because Republicans control the Senate and therefore the rules of the game, there is nothing House managers could do to stop the other side from calling witnesses. Trying would not only be futile, it would look like an attempt to deny Trump his right to due process. The audience would react badly to that kind of perceived unfairness.

The best bet for House managers is to treat Trump’s witnesses as an irrelevant sideshow — a classic red herring. They should give the case that Trump’s attorneys make the attention it deserves — none, sending a clear signal that it isn’t worth a response. Sometimes the most devastating cross examination consists of these seven words: “I have no questions for this witness.”

If the proceedings truly head into carnival territory, the managers can also appeal to Roberts. The chief justice is empowered to make rulings and could impose some limits on a process run amok. Conventional wisdom says he is unlikely to inject himself into the proceedings. He is cautious by nature, and the fact that a majority of senators can overrule him is a humiliating prospect. But it is hard to see him enabling the shredding of custom, decorum and common decency. That is a mockery of the judicial system that an institutionalist like Roberts would find intolerable.

But prosecutors should not look to Roberts as their savior. They should save themselves, and their case, by dispensing with whining and grandstanding. A smart prosecutor lets the damning, dramatic facts do the talking. Which brings me to another piece of advice my supervisor gave me all these years ago. The side with the story that most closely resembles reality is the side that wins.

Twitter: @larabazelon