Washington (CNN) Accuracy appears to be a secondary concern when you're the press secretary in the Trump White House, where the primary role is performing for an audience of one. But as Sarah Sanders approaches one year behind the White House podium, the questions about her credibility are growing louder.

"I'm very comfortable with my credibility," she told CNN's Chris Cuomo Wednesday night, before launching into an argument minutes later defending President Donald Trump's unproven claim that there was a broad conspiracy by federal law enforcement to spy on his campaign.

The episode perfectly encapsulated the challenge Sanders faces on a daily basis -- being the public face for a president who frequently contradicts himself and those who speak for him, leading many to question how much longer she can last in a role that tests her credibility on a regular basis.

Sanders' role in the West Wing was described to CNN by a half-dozen people familiar with it.

Sanders has told allies and confidantes that she doesn't expect to remain in her role as press secretary forever because the demanding schedule doesn't pair well with raising three young children. A central question to how much longer she lasts in the position revolves around how long she believes she can maintain her credibility and be effective for the President, two people familiar with her thinking said, but she has told friends she wants to serve at least a year in the position -- possibly longer, at the pleasure of the President.

Another person close to Sanders said the midterm elections would be a natural time for Sanders to leave the intense role -- an end date that half a dozen other senior officials have considered as well.

"She's not as frustrated as people on the outside may think," said one Republican friend who frequently talks with her, speaking on condition of anonymity to not alienate her. "She believes the President is often treated unfairly and she's fighting the good fight."

On the job learning

Sanders learned how to challenge Trump by watching Hope Hicks. In Oval Office meetings, Sanders quietly observed how Hicks picked her battles with their mercurial boss -- and took notes -- two sources familiar told CNN. If Trump had a wild idea that she thought might cause a serious backlash, Hicks would sometimes suggest another course of action. If he was in the middle of dictating a blistering tweet that she knew would generate negative headlines for days, Hicks would recommend wording it this way or that way instead. Sometimes he listened, and sometimes he didn't. But as time went on, Sanders learned how to join forces with Hicks to cajole the President into taking what they believed was the best path. With Hicks' March departure, Sanders has been on her own in dealing with the volatile president.

Hicks served as a sounding board for the President and was one of the few people in his inner circle that understood his personality. One of her primary roles in the West Wing was controlling his media access and she always sat in during his interviews with reporters. When she left, that responsibility fell to Sanders, who is now seen by her colleagues as the conduit for press access, fielding most inquiries that come his way as her profile has risen in the West Wing since Hicks left.

Although Sanders has taken over some of Hicks' main responsibilities, sources familiar with their relationship told CNN Trump does not have the same personal relationship with her that he had with Hicks, who he sees as a family member. He does not, for example, shout out for Sanders from the Oval Office in the way that he did for Hicks, which usually amounted to a "Hope! Hopester! Get in here!" Though he and Sanders speak regularly, their conversations are all business.

Path to the podium

Sanders assumed the podium July 21, 2017, after serving as deputy press secretary for the first six months of the administration and has become a trusted confidante of the President's. He is more satisfied with the briefings since she was pushed in front of the press corps when her predecessor, Sean Spicer, stepped down last July after Anthony Scaramucci was briefly hired as the communications director.

Trump had grown exasperated by Spicer's combative press briefings, which he watches closely from his private dining room off the Oval Office. He thought Spicer bungled answers to difficult questions, and privately encouraged him to hold the briefings off camera or let one of the deputies do it. Trump told other aides he thought Spicer seemed mad at the world when he was addressing reporters, now noting how Sanders can push back on the press corps without losing her cool.

"She's got a great face," Trump, who is obsessed with aesthetics, once remarked of Sanders. "Perfectly round."

Trump, meanwhile, had often remarked on Spicer's ill-fitting suits.

In a West Wing rife with infighting, Sanders is one of few who is generally well-liked and respected by her colleagues that constantly leak damaging information on one another to reporters. When she first stepped into the press secretary role, a senior official remarked how they appreciated that Sanders would approach staffers on their areas of expertise when she expected questions on that subject during the briefing.

Before facing reporters, Sanders goes through extensive preparation that can stretch two hours long and include multiple officials. Though Spicer surrounded himself more than two dozen staffers in the time leading up to the daily briefing, Sanders prefers a focused, tight-knit group. She typically meets with White House chief of staff John Kelly or Trump in the Oval Office beforehand, going over her scripted answers and soliciting their input.

Credibility at stake

JUST WATCHED Sanders: No question there was foul play in FBI Replay More Videos ... MUST WATCH Sanders: No question there was foul play in FBI 01:17

But all the prep in the world doesn't change the fact that in front of the cameras, Sanders is often put in the difficult position of putting her credibility on the line time and time again for a President who speaks for himself.

In March, she said Trump and his national security adviser H.R. McMaster had a "good working relationship." He was fired a week later.

That same month she told reporters that -- as far as she's aware -- Trump didn't know his lawyer Michael Cohen paid a porn actress for her silence about an alleged sexual encounter. Rudy Giuliani later said he did.

And in recent days, Sanders has been pressed with questions about a misleading statement drafted aboard Air Force One last summer regarding Donald Trump Jr.'s meeting in Trump Tower with Russian officials. Though Sanders said last fall that Trump did not dictate the statement, but offered input "as any father would," his legal team has since told federal investigators he did dictate it. Sanders was on that flight, but she has refused to explain the inconsistency.

Sanders seeks to avoid being undermined by offering answers that can't be contradicted -- cycling through vague phrases like, "Not that I'm aware of." "I can't say with 100% certainty" and "The President has made his position very clear."

Though critics argue that Sanders is willingly speaking on behalf of the administration, tensions over a lack of information have, at times, reached a boiling point. After the staff secretary Rob Porter was accused by two ex-wives of physical abuse, Sanders read glowing statements defending Porter. But as the story unfolded it became obvious Kelly and White House counsel Don McGahn knew more than they had initially claimed. Both McGahn and Kelly were generally aware of the allegations against Porter before he stepped down, multiple sources told CNN, making them central players in the saga.

JUST WATCHED WH on Trump's Porter tweet: Not taking a side Replay More Videos ... MUST WATCH WH on Trump's Porter tweet: Not taking a side 01:40

Sanders, frustrated with having initially defended Porter, engaged in a West Wing yelling match with McGahn, who she believed wasn't giving her enough information about the ordeal. She refused to face reporters again if she didn't get answers.

"We're giving you the best information that we're going to have," Sanders said during a briefing in the following days. "Obviously the press team's not going to be as read-in, maybe, as some other elements, at a given moment, on a variety of topics. But we relay the best and most accurate information that we have, and we get those from those individuals."

Though tensions later cooled, Sanders has had a troubled relationship with the counsel's office ever since, sources familiar with the relationship said.

Though she returned the White House to a more regular on-camera briefing schedule than the end of Spicer's tenure, Sanders has held fewer briefings in recent weeks compared to her first few months.

It appears to be a reflection of how the President is intent on driving the White House coverage himself, through tweets and brief question-and-answer sessions with reporters.

While several officials say Trump is generally pleased with Sanders' performance, particularly how she tangles with reporters in the briefing room, the President believes he is the best voice of his administration. He remains unmatched in his ability to dictate coverage with his remarks -- on Twitter and in public -- in a way that neither she nor any of his aides can.