Sen. Elizabeth Warren (D-MA) took the lead in a new Des Moines Register Iowa poll on Saturday night, marking the first time the Massachusetts senator led both former Vice President Joe Biden and Sen. Bernie Sanders (I-VT) in the first caucus state in the poll.

According to the new survey, Warren leads at 22 percent, with Biden following at 20 and Sanders at 11 percent. No other candidate reached double digits but South Bend Mayor Pete Buttigieg followed at 9 percent, with Sen. Kamala Harris (D-CA) at 6 percent to round out the top five. Additionally, the poll found that Warren was drawing the support of 32 percent of those who say that they caucused for Sanders in 2016 and that she narrowly led him among voters under age 35.

“It’s the first time we’ve had someone other than Joe Biden at the top of the leader board,” J. Ann Selzer, president of Selzer & Co. which conducted the poll, said.

The poll comes as Sanders’ campaign has shaken up its staff in two early voting states.

The Independent from Vermont remains at or near the top of most primary polls and no other candidate has matched his fundraising and grassroots organization capacity. But even with his staying power, he has been increasingly eclipsed in the eyes of opponents by Warren as the main progressive force in the race.

Stuck in this position, Sanders’ campaign has shuffled staff in two early crucial primary states, where his operation replaced their New Hampshire state director and Iowa political director and a deputy Iowa field director. Some sympathetic to Sanders have noted that changing around staff at this juncture obviously demonstrates a sign of dissatisfaction with the senator’s status in the race. He continues to build and demonstrate a massive legion of support, hitting one million donors this week—a milestone no other candidate has reached yet.

That explains why now, internally, the only message that Sanders’ team would convey is confidence, with one surrogate noting that the Vermont senator’s resources are so vast that his campaign will kick into an even higher gear with an anticipated television ad buy in the early states.

“There are two advantages that Senator Sanders has,” Rep. Ro Khanna (D-CA), a campaign co-chair, told The Daily Beast. “He’s got the largest grassroots fundraising base. He hasn’t yet gone on television in the early states. He’s going to go on television in the early states. Some of the other candidates have already been on television. Once he goes on television, he’s going to be able to sustain it and have more resources to do that not just in the early states but in places like California.”

Despite Khanna’s claim about the senator’s plans, a spokesperson for the campaign later quickly denied that there would be an ad buy soon.

Whether or not there will be, Sanders’ campaign for now is chalking up the staffing changes to isolated incidents and natural growing pains through the course of a campaign.

“ Pundits in the Beltway might not believe it, but Bernie Sanders’ campaign in Iowa is out-organizing the entire field, and this is all powered by the most grassroots volunteers and donors of any campaign in the country. ” — Iowa State Director Misty Rebik

For instance, there had been some annoyance with how Joe Caiazzo had been running the New Hampshire operation. That was made clear by reported cheering last weekend when members of the state steering committee heard that he had been reassigned to Massachusetts.

Sanders dominated in his neighboring state in the 2016 primary, which helped propel his campaign to become a major threat against Hillary Clinton. Now, he is locked in a tight contest with Biden and Warren, according to the Real Clear Politics average of recent polls.

In Iowa, the campaign parted ways with political director Jess Mazour, though in that case there was far less apparent open negativity about the way in which she was running things.

“We’ll continue to make moves that we feel best position this campaign to win,” campaign manager Faiz Shakir said in a statement to The Washington Post about the move. He did not immediately respond to a request for comment for this story.

Sanders famously fought Clinton to a near-draw in the Hawkeye State in 2016, portending the strength of his campaign to come. Though famously difficult to poll, he is now basically deadlocked in second place with Warren behind Biden. Yet his campaign announced on Friday that they had surpassed one million voter contacts in the state, another sign of the strength of their ground operation that they hope pays off next year.

“Pundits in the Beltway might not believe it, but Bernie Sanders’ campaign in Iowa is out-organizing the entire field, and this is all powered by the most grassroots volunteers and donors of any campaign in the country,” Iowa State Director Misty Rebik said in a statement.

The purgatory status for Sanders campaign was demonstrated by an Iowa poll on Saturday night that showed him slipping. But there’s no doubt that he remains among one of the top contenders for the nomination, with other campaigns even saying as much. In a memo on Saturday, Sen. Cory Booker’s (D-NJ) campaign manager issued an urgent plea for fundraising in the next 10 days to effectively keep him in the race. Within it, he noted that Biden, Sanders, Warren and South Bend Mayor Pete Buttigieg are the four campaigns with enough resources to compete for the long haul currently.

“ Warren has completely out campaigned him. I scratch my head and go how is Bernie going to get around her? ” — Unaffiliated Democratic consultant

While he still is among the top tier of candidates in the crowded field, there is some evidence to suggest that Sanders’ opponents are more interested in training their fire on Warren for now. On Thursday, a number of the other presidential contenders leveled various criticisms at the Massachusetts Democrat, with Buttigieg explicitly invoking her by name to say that she was “extremely evasive” in answers about Medicare for All, the primary policy plank that has animated Sanders’ political vision for years.

Warren also won the support this week of the Working Families Party, a left-wing political outfit that supported Sanders in the last primary. The voting process, and the lack of a revealed tally, has led to some acrimony from Sanders supporters who have leveled charges that the leadership of WFP essentially commandeered the process to back Warren.

Maurice Mitchell, WFP’s national director and Nelini Stamp, national organizing director at WFP, wrote about the selection process in response to criticism that they had heard. In turn, they also urged that supporters remain positive about both candidates.

“Both Warren and Sanders are fighting for the world we want to see, and both have brought new and vital ideas into the political debate,” they wrote. “Our endorsement of Senator Warren does not diminish our respect for Senator Sanders, and to be clear, we’re going to be relentlessly positive about both of them in the months ahead.”

Sanders and Warren appear poised to remain “relentlessly positive” about each other as well—as neither side has demonstrated a willingness or desire to go negative. In fact, Khanna defended both of them against Buttigieg’s attack line in a tweet on Friday.

But underscoring some of the recent moves by the campaign appears to be a notion from some that Warren is outflanking Sanders for now. And it remains to be seen whether she is having an ephemeral moment or steadily climbing her way to the nomination.

“Warren has completely out campaigned him,” an unaffiliated Democratic consultant familiar with the campaign told The Daily Beast. “I scratch my head and go how is Bernie going to get around her?”