President Donald Trump gestures while giving the commencement address at...

President Donald Trump gestures while giving the commencement address at the U.S. Coast Guard Academy, Wednesday, May 17, 2017, in New London, Conn. Credit: AP

One of the more surreal features of a White House effort to drown out former FBI Director James Comey’s Senate testimony on Thursday comes in the form of a textbook campaign ad against Comey — who is not running for office.

“As head of the FBI,” says a female narrator, feigning the tones of a newscaster, “James Comey put politics over protecting America.”

Quotes from various news sites adorn the message. The ad propagates the claim that he focused on election meddling at the expense of fighting terrorism.

Ominous music plays as the punch line is delivered: “James Comey. Just another DC insider. Only in it for himself.”

If enough voters absorb this agitprop, maybe they’ll look for Comey’s name on their November ballots so they can vote against him.

But, again, the fired lawman isn’t running for anything.

It is hard to recall a previous organized offensive like this against a congressional witness.

This attack ad, from the Great America Alliance — a political committee for President Donald Trump — is due to run on CNN and Fox during the hearing. It is meant to impugn Comey’s credibility when he suggests Trump tried to kill a probe of his ex-national security adviser Michael Flynn.

The art of remote heckling also comes into play if Trump, as many expect, responds to Comey in real time by jeering via Twitter during the Senate Intelligence Committee session.

Clearly the president and allies don’t think it sufficiently serves their purposes for a Republican-run committee to conduct questioning in a way that will put Comey on the spot and give the White House the benefit of the doubt.

Comey, of course, will be pressed on why he didn’t tell Congress at the time — as reported since the firing — that Trump told him of the Flynn probe: “I hope you can let this go.”

The word perjury stemming from previous statements will be tossed around. GOP lawmakers are expected to ask Comey about former President Barack Obama and former Secretary of State Hillary Clinton.

Having the president tweet during the hearing would draw attention to Trump. In theory, this could backfire.

Imagine if a sworn witness keeps his smartphone handy, reads aloud the Trump tweets, looks into the TV camera, and shouts: “Hey Donald! That’s nonsense!” before the gavel falls and the chairman imposes order.

That would make for powerful reality television, very different from “The Apprentice.”

Of course, Team Trump could simply trust citizens to watch the testimony, listen to the exchanges and decide for themselves whom to believe on the matters in dispute.

But that’s unlikely to make anyone’s political playbook.