A striking new poll found Bernie Sanders surging past Hillary Clinton in Iowa
Sanders was the choice of 41% of likely Democratic caucus participants, compared to 40% for former Secretary of State Hillary Clinton, according to the Quinnipiac University survey.
The results are just the latest stunning numbers for Sanders as he seeks to topple Clinton, who is backed by virtually the entire Democratic establishment.
Sanders previously overtook Clinton in New Hampshire, another key early-voting state that neighbors his home state of Vermont.
A Sunday NBC/Marist College poll of New Hampshire also found Sanders with 41% support among Democratic voters, but with a wider, nine-point lead over Clinton, who had 32% of the vote.
Clinton jumped into the race as the overwhelming favorite for her party's nomination, but her campaign has endured a difficult summer.
Notably, she has struggled to address the controversy over her email use as secretary of state. Clinton exclusively used a private server for her State Department work between 2009 and 2013, raising questions over whether classified information was properly handled. The FBI is now reportedly looking into the issue.
Tuesday marked a sharp turnaround in how Clinton addressed the email flap. As recently as Monday, she was refusing to apologize and insisting her email system was appropriate. But she reversed herself and is now offering a direct apology to her supporters while admitting she made a mistake.
"I wanted you to hear this directly from me," Clinton said in her message to supporters. "Yes, I should have used two email addresses, one for personal matters and one for my work at the State Department. Not doing so was a mistake. I'm sorry about it, and I take full responsibility."
However, Democratic hand wringing over Clinton's campaign has continued to bubble up, especially because Sanders, a self-described democratic socialist, is not viewed as a strong general-election candidate.
Party leaders are increasingly looking at the potential for Vice President Joe Biden to enter the race. A New York Times story out Thursday even speculated about whether Secretary of State John Kerry, former Vice President Al Gore, or Sen. Elizabeth Warren (D-Massachusetts) could leap into the fray to stop Sanders.
Clinton's future isn't completely tied to New Hampshire and Iowa, however, and she has built up a gigantic fundraising edge and campaign infrastructure that would serve as a bulwark against any challenger, especially in later primary states that have more diverse electorates.