Get breaking news alerts and special reports. The news and stories that matter, delivered weekday mornings.

Bernie Sanders has taken a narrow lead in Iowa and Pete Buttigieg has fallen, according to a new poll, but the race remains essentially a four-way jump ball with less than a month to go before the critical first-in-the-nation caucuses.

The Des Moines Register/CNN/Mediacom Iowa poll, released Friday evening, shows Sanders with 20 percent support among likely Democratic caucus-goers, a comeback after his October heart attack.

Right behind Sanders is fellow progressive Sen. Elizabeth Warren of Massachusetts at 17 percent, followed by Buttigieg, at 16 percent, and former Vice President Joe Biden at 15 percent.

It's a nine percentage points drop for Buttigieg, the former mayor of South Bend, Indiana, from the first-place 25 percent support he registered in the November Des Moines Register poll. And it's a weak showing for Biden, who remains the leader in most national polls.

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

But all four candidates at the top of the pack are within the margin of error of each other and no one has pulled ahead, meaning the Feb. 3 caucus is still anyone's game.

"There's no denying that this is a good poll for Bernie Sanders. He leads, but it's not an uncontested lead," pollster J. Ann Selzer, who has long been considered the most accurate pollster of Iowa's unpredictable caucuses, told the Register.

And while the percentage of people who say they have made up their mind has risen, it's still only 40 percent of likely caucus-goers. "The caucus process is an invitation to keep an open mind," Selzer said.

The other Democratic candidates, meanwhile, once again failed to demonstrate any major growth in support.

Minnesota Sen. Amy Klobuchar has been garnering renewed attention but held steady at 6 percent. New Jersey Sen. Cory Booker remains at 3 percent and billionaire Tom Steyer and Hawaii Rep. Tulsi Gabbard are both stuck at 2 percent.

Businessman Andrew Yang saw his support tick up two percentage points to 5 percent.

Caucus rules require candidates to reach a threshold of 15 percent support in each of the state's nearly 2,000 precinct caucuses to be considered "viable," or their supporters are forced to "re-align" to another candidate, so second choices are important.

Warren and Buttigieg are the top second choice for likely caucus-goers, but respondents said they were actively considering all four leading candidates at roughly equal levels.

The poll of 701 likely Iowa Democratic caucus-goers was conducted Jan. 2-8 it has a margin of +/- 3.7 percentage points.