More top Democrats, including 2020 frontrunner Joe Biden, have accused Donald Trump of being a white nationalist as part of a growing chorus of condemnation following the mass shooting in El Paso, Texas, that targeted Hispanics.

Biden, who has consistently led in recent polls, was speaking about the president’s actions along with others Democrats at a fundraising dinner late Friday night in the early voting state of Iowa when he declared: “Let’s call this what it is. This is white nationalism, this is white supremacy.”

Another candidate, Pete Buttigieg, mayor of of South Bend, Indiana, also accused Trump at the same event of “coddling white nationalism”.

The latest comments come after Trump has been roundly condemned for his racist rhetoric, especially over the issue of immigration, which many observers have linked to a rise in white nationalist attacks.

The suspect in the El Paso mass shooting explicitly confessed to police that he was targeting “Mexicans”, authorities have said, confirming that the crime – believed to be the deadliest attack against Latinos in the US in recent history – was motivated by racism. In an online manifesto allegedly posted by the shooter just before the attack, the attacker said he feared a Hispanic takeover of Texas.

Other Democrat candidates had previously condemned Trump for white nationalism, including former Texas congressman Beto O’Rourke, the Massachusetts senator Elizabeth Warren, the New York senator Kirsten Gillibrand and the Vermont senator Bernie Sanders.

Democrats have especially focused on Trump’s use of language around immigration where he has called immigrants “rapists” and “criminals” and accused them of launching an “invasion” of the US. That language was echoed in some of the words used by the El Paso shooter.

Biden and Buttigieg were speaking at the Wing Ding dinner in Iowa, once a low-key fundraiser that served up chicken wings and raised money for Democratic candidates and nearby county parties. It is now an event that has grown in stature in the state that kicks off presidential primary voting and the tone this year was one of full-front attack on Trump.

Buttigieg mocked Trump’s background in television, saying he wasn’t sure if its current occupant had turned the White House into a “reality show” or a “horror show”.

“What we’re going to do is pick up the remote and change the channel,” Buttigieg, the youngest presidential candidate, proclaimed to sustained cheers.

Pete Buttigieg speaks at the Wing Ding dinner in Clear Lake, Iowa, on 9 August. Photograph: John Locher/AP

The candidates at the dinner overlapped with messages of how Trump had spread hate and fear nationwide. But a few also offered stern warnings that beating Trump in 2020 will be tough.

Sanders said Trump will win unless Democrats have an argument that “speaks to the pain and reality of the working families of this country”.

Former Colorado governor John Hickenlooper noted that Trump’s approval rating was about 42%, slightly lower than former presidents Ronald Reagan and Barack Obama before they won re-election. He also said neither Reagan nor Obama had “an economy as strong as the one today”.

Hickenlooper said the Democrats need to look at the nation’s history to beat Trump and swiped at the numerous senators seeking the White House, saying no senator has ever beaten a sitting president, only former governors have because they were closer to their constituents.

Some of the loudest applause came for Warren, who tailored her message to her rural surroundings, saying she would stand up for small farmers against “big ag” interests.

Elizabeth Warren speaks at the Wing Ding dinner in Clear Lake, Iowa, on 9 August. Photograph: John Locher/AP

“Trade war by tweet is not working for our farmers,” she said of Trump’s using Twitter to announce tariffs on China, which has stung international markets. “I promise you this, when I’m president, when I negotiate a trade deal there will be independent farmers at the table.

The Minnesota senator Amy Klobuchar poked fun at the parade of candidates taking the stage one after another and forcing everyone to keep their speeches short: “Last time I had 20 minutes, and this time I have 20 candidates.”

Some of the candidates who ran longer than their allotted five minutes including the evening’s final speaker, Biden, were subjected to musical cues trying to play them offstage, just like the Oscars.