DES MOINES, Iowa (Reuters) - Former Vice President Joe Biden said he was not taking his front-runner status for granted as he returned to Iowa on Thursday, ahead of a wave of rival Democratic presidential contenders who will in coming days visit the state that starts the party’s nominating contest.

Before the weekend is out, more than 20 contenders will attend the Iowa State Fair and speak at a state Democratic Party dinner, giving Iowans a full picture of the field.

Next February’s caucuses in Iowa will kick off the process of selecting the person to run against Republican President Donald Trump in the November 2020 general election.

Speaking to a sun-baked crowd at the fair, Biden said: “We must defeat this president to change the trajectory of this country.”

For Biden, the trip to Iowa gives him an opportunity to try and cement his lead in opinion polls over the rest of the field, one that appeared greatly endangered after he turned in an uninspiring performance at the first Democratic debate in Miami.

But Biden appeared to have held his own at last week’s debate in Detroit against attacks from others on the stage. And his numbers in public opinion polls have largely returned to where they were before the Miami debate.

At the state fair, Biden largely stuck to his campaign stump speech without mentioning the mass shootings in El Paso, Texas and Dayton, Ohio last weekend that shocked the United States.

In response to Democratic calls for action on gun control legislation, Republican Senate leader Mitch McConnell suggested he was open to bipartisan discussions on possible restrictions on assault gun sales and background checks. But he refused to call the Senate back early to consider new gun legislation.

After his appearance, Biden told reporters he believes Congress can pass a new ban on assault weapons.

Slideshow ( 5 images )

“We can get it done, and we can get background checks done,” he said. “We can get it done because the public is finally at a point where they are sick of it. Sick of it.”

Biden suggested he understands that his front-runner position could be tenuous, and said he would continue to campaign in Iowa to amass support.

“It’s early,” Biden said. “It’s way early.”

An poll of Iowa Democrats released by Monmouth University on Thursday showed Biden with 28 percent of the vote, with progressive rival U.S. Senator Elizabeth Warren, who has been building momentum in the state, second at 19 percent.

In his speech at the fair, Biden, 76, at times fumbled parts of his delivery, saying at one point that in comparison to Trump, Democrats “choose truth over facts.”

Sherry Leydens, 72, of Ankeny, Iowa said she had come to the fair to see Biden, who she said she will support in the caucuses. “He is the best person to take on Trump,” she said.

But Mickey Long, 47, of Burlington, Iowa said with others gaining, “it kind of made me rethink things.” Once a Biden supporter, she was now considering Warren, Long said.

Slideshow ( 5 images )

MAKE OR BREAK EVENT

For Biden, a longtime senator and the vice president under President Barack Obama, the state fair holds particularly potent memories. It was here in 1987 when his first presidential campaign began to implode over allegations of plagiarism.

He ran for president again in 2008, but his campaign ended after he fared poorly in the Iowa caucuses.

The fair has also proved to be thorny for others. In 2011, Republican presidential candidate Mitt Romney told a heckler in the crowd that “corporations are people, my friend” — a line that haunted him during the rest of the 2012 presidential race.

That same year, a photo of Republican candidate Michele Bachmann eating a foot-long corndog sparked an online uproar.

There have also been made-for-TV moments that have bolstered campaigns. In 2015, Trump’s visit to the fair via helicopter stole the thunder from other Republicans and helped draw more attention to his insurgent candidacy.

The other candidate to appear at the fair on Thursday stood in marked contrast to Biden. Montana Governor Steve Bullock only entered the Democratic race in May and remains an unknown to many.

Bullock made light of his anonymity, telling the crowd that he wanted to move up from “35” to higher on their candidate lists.

For candidates such as Bullock, who are polling near the 1 percent mark, the weeks ahead before the next Democratic debate in September will be crucial to their continued viability.

On Friday, Democratic candidates such as former U.S. Housing Secretary Julian Castro and outsider candidates Marianne Williamson and Andrew Yang will speak at the fair.

And later in the evening, virtually every member of the crowded field will attend the traditional “wing ding” dinner in Clear Lake, Iowa.

Noticeably absent is former U.S. Representative Beto O’Rourke, who canceled all of his Iowa events in the wake of the shootings in El Paso, his hometown.

The majority of the field will also participate in a gun-violence forum on Saturday sponsored by Everytown for Gun Safety, a gun-control advocacy group founded by former New York Mayor Michael Bloomberg.