President Joe Biden has suffered a bruising in South Dakota, after failing to attract about a quarter of votes in the Democratic Party’s primary election.

In March, Biden and his Republican rival, former President Donald Trump, both received enough delegates across multiple primary votes to secure their parties’ nominations for November’s presidential election.

However, the primary season is still ongoing, and in some states voters are supporting other candidates to express their opposition to the presumptive nominees, despite them being all but confirmed for the election.

In South Dakota, Biden won the primary with 74.6 percent of the vote on June 4, the Associated Press reported. At the time of writing, with 99 percent of votes counted, that represented 13,365 votes. Despite Biden’s electoral success, some one in four Democratic voters in the Mount Rushmore State did not vote for him.

South Dakota’s primaries are partially closed, meaning that only members of the Democratic Party and registered independents can vote in the Democratic primary.

Newsweek has contacted a representative for Biden for comment by email outside business hours.

Thomas Gift, who heads the Centre on U.S. Politics at University College London in the U.K., told Newsweek that those voting against Biden were not “representative” of the Democratic electorate and should not concern him too much.

“The fact that Biden already has the nomination clinched means that voters still motivated to show up at the polls aren’t at all a representative cross-section of the Democratic electorate,” he said. “There will inevitably be a higher percentage of disaffected partisans who come to the ballot box merely to make a point by signaling their discontent. While Biden certainly wishes his margins were larger, it’s not something his advisers will lose too much sleep over.”

It is not the first time Biden has faced opposition from members of his own party. In May, he won the Kentucky Democratic primary with 71.3 percent of the vote. With some 30 percent voting against him, it stands as the fifth-worst primary result of the 2024 cycle.

In the Kentucky primary, 17.9 percent of voters selected the “uncommitted” option, and 13.3 percent did so in Michigan, with some saying they were protesting Biden’s response to the latest war between Hamas and Israel.

Biden’s approval rating has also been poor recently. It has averaged 38 percent for months, according to the polling aggregator FiveThirtyEight, and Newsweek reported in May that Biden is the least-popular president in 75 years.

The Democratic incumbent is not the only candidate contending with protest votes. His Republican rival has also faced discontent in some GOP state primaries. In May, former South Carolina Governor Nikki Haley, who dropped out of the presidential race in March, won 22.7 percent of the vote in Maryland and 18.2 percent in Nebraska. While Trump won the primaries with a resounding majority, the results showed that he did not have the full support of Republicans in those states.

After the Democratic Party’s primary season concludes, Biden is set to face Trump on November 5 in a rematch of the 2020 election. It is expected to be a close race.

Update 06/05/24, 6:24 a.m. ET: This article was updated to include comment from Thomas Gift.