NORRISTOWN, Pa. — A witness sobbed, burning through tissues while she testified that the famous man gave her a pill and touched her as her vision blurred. Attorneys stalked across the well of the courtroom, voices booming in scorn and disgust.

The drama unspooling in a creaky old courtroom here in this Philadelphia suburb is a trial that once would have seemed unimaginable, a reckoning for a comic legend who not so long ago embodied an ideal of wholesome fatherhood. Bill Cosby’s days as America’s biggest television star are long behind him. But as he nears his 80th birthday, legally blind and leaning on a cane, he is the focal point in one of the highest-profile criminal trials in recent memory.

The aging entertainer listened intently Monday, occasionally clenching a fist or wincing, as attorneys offered competing visions of him on the opening day of the jury trial in his sexual assault case. A capacity crowd jammed into the courtroom, filling every seat in eight long rows of wooden benches. News helicopters hovered outside.

Cosby is accused of drugging and sexually assaulting Andrea Constand, an operations manager for the Temple University women’s basketball team, at his suburban Philadelphia home in 2004. But the first day of testimony was dominated by an emotionally charged appearance by another woman whom prosecutors called in hopes of establishing a pattern of illicit behavior by the actor.

Kelly Johnson, an assistant to Cosby’s personal-appearances agent at the William Morris agency in the 1990s, wept while recounting an afternoon in 1996 when she said the comedian summoned her to his bungalow at the swanky Hotel Bel-Air in Los Angeles. Johnson said that Cosby had invited her there “in a Dr. Huxtable kind of way” to offer career advice.

When she arrived, Johnson testified, Cosby was wearing a bathrobe. He urged her to take a white pill to relax, she said, opening her right hand on the witness stand to mimic the offer.

“Would I do anything to hurt you?” she said Cosby told her. “Trust me.”

Johnson, who was 34 at the time, didn’t want to take the pill, even hiding it under her tongue. But, she said, Cosby ordered her to open her mouth, then swallow. She felt “intimidated,” she said, because Cosby was the biggest client of the agency where she worked. She did what he said.

Confused, she went to the bathroom, where she found a huge array of prescription pills, she said. But her vision had gone fuzzy, and she couldn’t read the labels. Moments later, she said, she awoke in bed with Cosby, her dress pulled down from its top and up from its hem, exposing her breasts and her genitals. Cosby, she said, poured lotion into her hand and forced her to stroke his penis.

“I remember wanting to cover myself and not being able to,” she said through a torrent of tears.

Johnson, now a project manager for a corporation in Atlanta, is the only former accuser whom Montgomery County, Pennsylvania, Judge Steven O’Neill, who is presiding over the case, is allowing to testify. In an aggressive cross-examination, Cosby’s attorney, Brian McMonagle, tried without success to get Johnson to admit that her public comments about the allegations before the trial were coached by Gloria Allred, a feminist attorney who represents about half of the 60 women who have accused Cosby of sexual misdeeds over five decades.

After the alleged assault, Johnson testified, Cosby called her boss, the prominent agent Tom Ilius, and demanded that she be fired. When she lost her job, she filed a workers’ compensation lawsuit and gave deposition testimony with a different date for the alleged assault. But she stood firm when McMonagle loudly confronted her about the discrepancy.

(The Post has previously reported on Johnson, who appeared on camera at a January 2015 news conference using the pseudonym “Kacey.” We are now using her name because she has testified in open court.)

PROSECUTION’S CASE TAKES SHAPE

Johnson’s testimony was the opening salvo in a prosecution case that came into sharper focus Monday morning during a searing opening statement by prosecutor Kristen Feden.

“This case is about trust, betrayal and the inability to consent,” Feden said, with a look of contempt on her face.

The prosecutor repeatedly stalked across the floor, pointing an accusatory finger within inches of Cosby as he sat leaning forward at the defense table. When Feden said that Cosby drugged Constand because he wanted to “gratify himself” without any chance of rejection, the entertainer balled his left hand into a fist and held it to his mouth.

Feden, who is African American, sought to separate the image of Cosby as a lovable, trailblazing African American comedian from the more sinister accusations at the heart of the case. She implored jurors not to think of Cosby as Dr. Huxtable, the character he portrayed on television.

The delicate issue of race has loomed over the case for weeks. Cosby’s daughter, Ensa, said before jury selection earlier this month that her father is a victim of a “public lynching.” Cosby’s attorneys accused prosecutors of trying to block African American jurors from being seated, an argument the judge rejected.

Feden, for the first time, revealed Monday that prosecutors plan to introduce evidence from a toxicologist who will testify that Constand’s symptoms on the night of the alleged assault are consistent with the effects of quaaludes. Cosby has said that he acquired quaaludes to give to women with whom he wanted to have sex.

In police interviews, Cosby has said that he gave Constand a dose of Benadryl, describing the pills to her as herbal supplements that he called “friends to help you relax.” Anticipating that defense, Feden told jurors that Cosby has also said that Benadryl could induce drowsiness, noting to police investigators that he takes Benadryl as a sleep aid when he’s on tour and that he wouldn’t appear on stage after ingesting the allergy medication.

“He knew what effect it would take,” Feden said.

COSBY’S DEFENSE

Feden’s scorn was matched in intensity by McMonagle, Cosby’s charismatic attorney. During his opening statement, McMonagle portrayed Constand as a schemer motivated by greed and a serial liar.

“The only thing that is worse than (sexual assault) is the false accusation of sexual assault,” McMonagle said in a booming voice. “It’s an attack on human dignity.”

Alternating between an intimate whisper and a window-rattling voice of doom, McMonagle, a former prosecutor, issued a scathing assessment of Constand, saying that she had been “untruthful time and time and time again.”

The biggest flaws in the prosecution case, according to McMonagle, are the various statements Constand made to police. In her first interviews, she said that she’d never been alone with Cosby before the night of the alleged assault and that she had no contact with him afterward. Later, according to McMonagle, she told investigators that she’d been alone with the star several times and had brought him gifts, such as bath salts and incense. And phone records, McMonagle said, show that Constand called Cosby 53 times after the alleged incident.

Even the circumstances on the night of the alleged assault have become muddied in Constand’s statements, McMonagle said. Initially, she told police that Cosby assaulted her after a dinner out at a restaurant with a group of people. Later, McMonagle said, she changed her story and said that the assault occurred when she was alone with the comedian at his home.

COSBY ANIMATED

Cosby entered the courtroom leaning on the arm of Keshia Knight Pulliam, the actress who played the character Rudy on “The Cosby Show.”

As the courtroom filled, the 79-year-old entertainer was animated and chatty, laughing and cracking jokes with his attorneys. Later, as Judge O’Neill instructed the jury, Cosby sat looking directly across the room at the seven men and five women who will decide whether he is guilty of three counts of aggravated indecent assault.

A few steps behind Cosby, and to his left, sat one of his primary pursuers, Allred.

The sequestered jury has been bused across the state of Pennsylvania from Pittsburgh. They were selected from a different county because of defense concerns about pre-trial publicity in Montgomery County, Pennsylvania, where the district attorney who is trying the case, Kevin Steele, pledged to reopen the Cosby investigation during his 2015 election campaign.

Three of Cosby’s accusers who will not testify – Victoria Valentino, Therese Serignese and Lili Bernard – arrived at the courthouse hours early. They had hoped to sit in the same room as Cosby, but there was no room for them, and they were ushered to a separate room with a video feed.

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