Elizabeth Warren leads Joe Biden in Iowa for the first time, according to a new poll in the early voting state.

The survey carried out by the Des Moines Register, Mediacom and CNN puts the Massachusetts senator at 22% with likely caucus-goers, to the former vice-president’s 20%.

They are well clear of the sprawling Democratic field. The Vermont senator Bernie Sanders placed third, with 11%, ahead of South Bend, Indiana, mayor Pete Buttigieg on 9% and the California senator Kamala Harris on 6%.

The New Jersey senator Cory Booker, who said on Saturday he would drop out of the race if a fundraising target is not met, was next with 3%, tied with the Minnesota senator Amy Klobuchar.

Harris said this week that she will go all-in on Iowa, aiming for a top-three finish.

Biden still leads the realclearpolitics.com national polling average, on 30% to Warren on 19% and Sanders on 16%. Buttigieg and Harris, on 6%, are the only other candidates with more than 3% support.

Most of the Democratic field is in Iowa this weekend, on Saturday for the Polk County Steak Fry and a People’s Forum. On Friday night, many of the candidates addressed an LGBTQ Presidential Forum.

The shadow of Donald Trump was never far away. At the Steak Fry, Warren called for the impeachment of the president and told the crowd: “I know what’s broken, I know how to fix it, and we’re building a grassroots movement to make it happen.”

Biden called for Americans to “pick our heads up, remember who we are, we are the United States of America”.

He also addressed Trump’s calls for an investigation into his family over business ties to Ukraine, amid swirling scandal over the president’s behaviour and visits by his lawyer Rudy Giuliani to the eastern European country.

“The fact of the matter is that that fellow in the White House knows that if we get the nomination we’re gonna beat him like a drum,” Biden said. “So be prepared for every lousy thing that’s coming from him.”

The poll also asked likely voters for their second choices, an important selection in the caucus system. It concluded that at least 71% of likely caucus-goers are at least considering Warren, ahead of Biden on 60%.

According to the poll, 32% of those who said they caucused for Sanders in 2016 now support Warren, indicating the strength of her surge among progressive Democrats.