The poll also shows incumbent Ernst with a 4-point advantage over Democrat Theresa Greenfield in the competitive Iowa race for U.S. Senate.
The Republican senator pulled ahead of Greenfield among likely Iowa voters, 46 to 42 percent, marking the first time Ernst has led Greenfield in the poll this year.
Greenfield and Ernst have largely polled evenly since the early summer, with last week’s Monmouth University poll showing both candidates supported by 47 percent of the state’s registered voters.
The poll of 814 likely Iowa voters was conducted by Selzer & Co. of Des Moines from Oct. 26-29. It has a margin of error of plus or minus 3.4 percentage points.
Saturday’s poll contradicts recent polls of Iowa voters, which have shown Biden and Trump locked in a tight race. A Monmouth University poll last week showed that 48 percent of Iowa registered voters support Trump and 47 percent support Biden.
Trump’s support in the state has surged among independent voters, while Biden has lost ground with female voters, according to the poll.
While Biden led with independents in the September poll, 50 percent to 38 percent, Trump has now won them back with 49 percent support to Biden’s 35 percent.
Among female voters in Iowa, Biden held a 20-point lead in September, but his lead has diminished to 9 percentage points, according to the poll.
The Register’s pre-election poll has been a critical marker of which candidates will carry the state, predicting a 7-point lead for Trump over Hillary Clinton in 2016 and a 7-point lead for Ernst over Democrat Bruce Braley in 2014.
Trump won the state by 9.6 points in 2016, and Ernst won by 8.5 points in 2014. Trump went on to run the table in the so-called blue wall states of the Midwest, delivering him the presidency.
Iowa has emerged as a critical battleground in Tuesday’s election. While Trump won Iowa by a wide margin in 2016, former President Barack Obama carried the state in both 2012 and 2008.
Both candidates are making last-minute visits to the battleground with only a few days to go before the election. Biden made a campaign stop at the Iowa State Fairgrounds on Friday, and Trump will hold a rally in Dubuque, Iowa, on Sunday.