Rep. Katie Porter (D-Calif.) got out her marker and scrawled a figure on the whiteboard beside her: $13 million.

“Do you know what this number is?” she asked Mark Alles, the former CEO of the pharmaceutical company Celgene, as he testified remotely before the House Oversight Committee on Wednesday. “Does it ring any bells?”

Alles could hardly get his answer out before Porter scribbled more math on the board. That multimillion figure — his total compensation in 2017 — was already 200 times the average income in the United States, the congresswoman pointed out. It got even larger, she said, after Celgene needlessly tripled the cost of a cancer medication, thus securing himself hefty bonuses in return.

“The drug didn’t get any better. The cancer patients didn’t get any better," Porter told him. “You just got better at making money."

As of early Thursday, the rapid-fire interrogation had been viewed more than 15 million times on Twitter — the latest in a long list of her viral cross-examinations meant to draw the public to some hidden machination of Washington or corporate America.

Yet in the past two years, these stunning exchanges at congressional hearings have themselves gained plenty of attention beyond Capitol Hill — especially when Porter pulls out what one person on Twitter dubbed “her mighty whiteboard of truth.”

By now, the scene is familiar, if never less enthralling: Porter leans into the microphone by her seat in a hearing room. She turns to the board on her left to scribble some numbers. And then, she begins pelting questions at a powerful man in front of her.

Last year, to Housing and Urban Development Secretary Ben Carson: “Do you know what an REO is?” she asked, before Carson confused the foreclosure term with a cookie brand.

In March, to Robert Redfield, director of the Centers for Disease Control and Prevention: “Do you want to know who has the coronavirus?” she asked, before he gave in and promised her free testing for all Americans.

On Wednesday, to Alles: “Do you know how much you personally received in bonuses?” she asked, before he reluctantly acknowledged it was half a million dollars.

Yet, Porter continued. Celgene had repeatedly raised the price for revlimid, a treatment for multiple myeloma, from $215 per pill in 2005 to $719 last year. So she demanded that Alles, who led the drug manufacturer until it was acquired last year, explain what had changed over that time period.

“Did the drug start to work faster? Were there fewer side effects? How did you change the formula or production of revlimid to justify this price increase?” Porter asked.

Of course, he didn’t need to answer. The details were laid out in a congressional drug pricing investigation published Wednesday, which concluded that prices were jacked up to hit revenue goals for shareholders and thus score bonuses for Alles and others.

It is this kind of clear, insistent inquiry that has made Porter — a consumer protection lawyer and former professor who studied bankruptcy law under Sen. Elizabeth Warren (D-Mass.) — so effective at grilling everyone from Mark Zuckerberg to little-known Trump appointees, all with a dry-erase marker and some simple math.

“No one has ever wielded a weapon as terrifying as Katie Porter’s whiteboard,” wrote Molly Wood, a public radio journalist and host of “Marketplace Tech.” “This is just a fact.”

“If you ever wonder why certain types of men don’t want to elevate women into power, this, right here, is why,” said Julie Rodin Zebrak, a political consultant and contributing writer for Washington Monthly. “This is what they fear: Katie Porter calls BS and has the receipts and it is a glorious sight to behold.”

After a two-minute clip of the interaction was posted online on Wednesday by the consumer rights group Public Citizen, at least half a dozen people chimed in to say Porter, whiteboard in tow, should moderate the next presidential debate.

Others aimed higher. “At this point, when Katie Porter runs for president in the next decade, she won’t need a vice president,” one person wrote. “Her vice president will be her dry-erase board.”

Even the Daily Caller, a conservative news site, gave her credit. “It did not end well for a big pharma exec when Rep. Katie Porter pulled out her white board,” the website tweeted.

As The Washington Post’s Renae Merle reported last year, Porter quickly drew notice within her first months in Washington for an “analytical” approach during hearings. The day before, the lawmaker said she often spends time studying a 70- to 150-page binder of background information compiled by her staff to prepare for difficult testimonies.

But for Porter, who is the only single mother in Congress, it’s all small potatoes compared to her three children at home in Irvine, Calif.

“I have never encountered a witness,” she said last week, during an appearance on “The Late Show with Stephen Colbert,” “that was even close to as difficult as any one of my children.”