In Pennsylvania, a key swing state in the 2024 presidential election, President Joe Biden was greeted with a “big red flag.”

New voter registration data in the Keystone State suggests Republicans are gaining ground on Democrats compared to 2020, although Democrats still hold the advantage. Pennsylvania is considered one of the few swing states that could determine the outcome of the election between Biden and former President Donald Trump in November.

In 2020, voter registration data showed that there were about 800,000 more Democrats than Republicans in Pennsylvania, even though Biden won the state by just over 80,000 voters (about 1.2 percentage points). As of last month, that number has dropped to just about 375,000, according to the data.

This year alone, 28,382 Democrats switched their party affiliation to the Republicans, while as of June 24, only 9,846 Republicans switched their party affiliation to the Democrats.

Jennie Sweet-Cushman, professor of political science at Chatham University, said Newsweek on Monday that this shift toward Republicans should be a “major warning signal” for the Biden campaign.

“The main rationale for his re-election seems to be that he has the best chance of beating Trump because he's done it before. Unfortunately, that was a narrow win in Pennsylvania. To do it again, he needs to keep his voters, and given the deterioration of his support among young voters, the enthusiasm gap and the rewarming of Republicans to Trump, it's becoming increasingly difficult for him to do that,” she said.

J. Wesley Leckrone, associate dean of social sciences at Widener University, said Newsweek on Monday that small shifts toward Biden or Trump could affect the outcome because the state is so divided.

“But this was a long-term realignment of the state, where people's party registration now more accurately reflects how they vote. The 2024 election in Pennsylvania will be won by party turnout and influencing independent voters,” he said.

Newsweek has emailed Biden's campaign team asking for comment.

The shifts largely reflect trends that have played out nationally in recent years. Rural voters switched from Democrats to Republicans. In suburban areas, particularly in counties near Philadelphia, Democrats gained ground.

In more rural areas in the west of the state, such as Lawrence, Cambria and Washington counties, Republicans have made the strongest gains, at least in percentage terms, over the past four years.

The biggest shift in absolute numbers, however, occurred in the Democratic stronghold of Philadelphia. In the state's largest city, there were 708,103 more Democrats than Republicans in 2020, but only 654,040 in 2024. This reduced the gap by 53,463 voters.

Suburban Democrats received better news. In Chester County, there were only 786 more Democrats than Republicans in 2020. By 2024, that number rose to 7,076. In Delaware County, there were 41,631 more Democrats than Republicans in 2020. That number rose to 57,536 this year.

Republicans also gained ground in the state's most contested districts, where Republicans alternately supported Democrats and Republicans.

In Northampton County, Republicans have secured 571 voters in 2024. In Erie County, Republicans have secured 470 voters. These two counties are expected to be closely watched before November, as Biden won Northampton County by just 1,233 votes and Erie County by 1,417 votes in 2020.

Leckrone noted that voters in the western part of the state had slowly adjusted their party affiliation to match their previous voting habits, while the Democratic realignment in the Philadelphia suburbs had occurred much more quickly.

“Current party registration numbers more accurately reflect people's voting behavior in recent election cycles. This is evidenced by the fact that Republicans were competitive in recent statewide elections, even though Democrats had a large lead among registered voters,” he said.

Sweet-Cushman said voter enthusiasm could also play a role in changing their registration.

“Republican voters in Pennsylvania are, on average, more likely to vote for Trump than Democratic voters are to vote for Biden. That probably means some of these new entrants are people who were suspicious of Trump in 2020 and are returning to the party in 2024. These people were probably never real Democrats,” she said.

Democrats have the “apparatus to succeed” in Pennsylvania because of the strong organization in the state, but they lack the message, she said. Democrats should focus on policy issues such as reproductive rights, environmental protection or family leave instead of “trying to harness them into an existential war for the soul of the country,” she added.

Leckrone pointed out that by emphasizing economic issues, Democrats should focus on appealing to working voters without college degrees.

Recent polls in Pennsylvania show the race remains close. An Emerson College poll of 1,000 registered voters conducted June 13-18 found Trump leading Biden by two percentage points (51 percent to 49 percent). A Redfield & Wilton Strategies poll of 456 likely voters conducted June 8-11 found Trump leading Biden by two percentage points (44 percent to 42 percent).