President Trump holds a nearly 20-point lead ahead of President Biden in Iowa, once considered the ultimate swing state, according to a new poll from Ann Selzer and the Des Moines Register. Trump’s strength in the state has only expanded since being convicted on 34 felony counts, Ms. Selzer finds. 

According to the poll, Trump is now winning 50 percent of the vote in the Hawkeye State, compared to Mr. Biden, who wins just 32 percent. Robert F. Kennedy Jr. takes 9 percent of the vote, and the rest of the survey respondents said they were not sure or that they would not vote. 

Trump’s lead ahead of the sitting president has expanded since he became a convicted felon. In February, the Selzer poll found Trump winning 48 percent of the vote to Mr. Biden’s 33 percent. 

One Trump-supporting poll respondent, Donald Share, told the Des Moines Register that the felony conviction only made him more enthusiastic to support the former president. “His convictions on these charges are part of the reason my mind is made up,” Mr. Share said. “The more they try to get him out of the picture, the stronger they make him. I, for one, believe that the charges are bogus.”

A decent share of both Trump’s and Mr. Biden’s supporters in Iowa say they could be persuaded to vote for someone else, the poll finds. In total, 24 percent of those who listed Trump as their first choice and 19 percent of those who listed Mr. Biden as their first choice say they may change their mind before November. 

Mr. Biden’s popularity and job approval rating as the sitting president are surely weighing heavily on his chances in Iowa, a state that his campaign barely contested in 2020 and looks highly unlikely to invest in this year. The incumbent president has not had a net positive approval rating in the Hawkeye State since March 2021. 

As of June 14, just 28 percent of Iowans approve of his job performance compared to 67 percent who disapprove. The demographic that most strenuously disapproves of Mr. Biden is a key Democratic Party constituency — young voters. Among those younger than 35, Mr. Biden’s approval rating is just 17 percent, compared to 76 percent who disapprove. 

Ms. Selzer’s poll has long been considered the gold standard for not just Iowa, but for the rest of the country. She has been praised as the only pollster to consistently choose not only the correct winners, but to get their margins of victory correct as well. 

In 2020, Ms. Selzer found that Trump was leading Mr. Biden by seven points in the weeks before the election, and Senator Ernst was beating her Democratic opponent by just four points on that same ballot. Trump went on to win Iowa by nine points and Ms. Ernst won re-election by six points. 

In 2014, when Ms. Ernst first ran for the Senate, Ms. Selzer’s poll found Ms. Ernst leading by seven points in the general election. She would later win her first Senate term by just more than eight percent. 

Ms. Selzer has accurately predicted — almost with a 100 percent success rate — the winner of each of the Iowa caucuses over the years. In 2008, she was questioned about her poll that found President Obama beating Secretary Clinton in that year’s Democratic caucuses — a poll that later turned out to be accurate.

Ms. Selzer also predicted the 2008 win on the GOP side of Governor Huckabee, the narrow 2016 victory for Mrs. Clinton over Senator Sanders, and the 2020 victory for Mr. Sanders. While the now-secretary of transportation Pete Buttigieg technically won the most delegates out of Iowa four years ago, Mr. Sanders narrowly won the popular vote, which Ms. Selzer predicted.