A flood of national and swing state poll results released in recent days show Vice President Harris seeing a decisive shift in her favor nationally and in critical battleground states. Her strength seems to come from her ability to unify and energize her own party’s base while also winning over independents — something President Biden was never able to do. 

In the last 48 hours, no less than half-a-dozen highly rated polls have shown that Ms. Harris has taken the lead in the national popular vote, as well as a slight lead in swing states like Pennsylvania. Arguably America’s most highly respected survey, the New York Times–Siena College poll, suggests Ms. Harris is mobilizing her core voters and convincing some undecided Americans to break her way. 

On Thursday, the September Times-Siena poll results were released, both in the form of a national survey and a poll of Pennsylvania, a state that is widely expected to decide the winner of the presidential election. 

According to those polls, Ms. Harris is beating President Trump by four points in Pennsylvania — 50 percent to 46 percent, which is outside of the poll’s three-point margin of error. The Keystone State survey was also done in partnership with the Philadelphia Inquirer. 

Her strength seems to come from her ability to shore up key Democratic constituencies. In Pennsylvania, she is beating Trump by 17 points among women voters, 57 percent to 40 percent, while Trump is beating her among men by a margin of 11 points, 53 percent to 42 percent. According to exit polls in 2020, Mr. Biden won women voters in Pennsylvania by a margin of 15 points.

Young voters, too, seem more energized in Pennsylvania than they were four years ago, or in the months leading up to Mr. Biden’s exit from the 2024 race. In the first half of 2024, some surveys showed Trump within single digits of winning the under-30 demographic in a rematch with Mr. Biden. 

Ms. Harris now has a 25-point lead among voters under the age of 30 in Pennsylvania. Nationally, Mr. Biden won that demographic by 20 points four years ago. According to the national survey conducted by the Times and Siena College, Ms. Harris is winning the youth vote by 21 points. 

While she has taken a lead in Pennsylvania, Ms. Harris is tied with Trump nationally in the popular vote, with both candidates at 47 percent. This can likely be attributed to Trump’s strengths with those same core Democratic constituencies — women, young voters, and minorities — across America, a strength he lacks among the same groups in Pennsylvania. 

Nationally, he is losing the female vote by 14 points, while winning the male vote by 12 points. Among voters between the ages of 18 and 29, he is losing by 21 points, and he is four points behind Ms. Harris with voters between the ages of 30 and 44. Among Black voters, Trump’s support clocks in at 15 percent — nearly double the 8 percent of the Black vote he won four years ago. 

The Times’s chief polling analyst, Nate Cohn, says the phenomenon of Ms. Harris leading in Pennsylvania but being tied with Trump nationally is unusual. He says that while his poll’s results may seem surprising, it actually tracks with some of the recent high-quality pollsters’ results — showing Trump being relatively strong on the national level while slipping in key Rust Belt states. Mr. Cohn mentions one poll that showed Ms. Harris leading in Pennsylvania, Wisconsin, and Michigan, but with just a two-point lead over Trump nationally.  

“I assumed it was partly or mostly because of timing. Many top national polls were taken soon after Ms. Harris announced her candidacy or just before the debate, while many high-quality state polls were fielded in between,” Mr. Cohn writes. “This suggested that the state polls might have caught Ms. Harris at the peak of her post-announcement surge, while the national polls caught her just before and after a political sugar high.”

Other polls released Wednesday found a similar strength for Ms. Harris in Pennsylvania, however. A survey released by Franklin and Marshall College — a respected outlet, and the first poll conducted in-state since the debate — found that Ms. Harris has a three-point lead over Trump, 49 percent to 46 percent. According to the poll, she is viewed as more trustworthy, more concerned about average Americans’ everyday needs, and better equipped to protect individuals’ personal rights than Trump. 

One poll that many observers were waiting for came early Thursday morning from Marist. While that outfit is not considered one of America’s best pollsters, it won a great deal of respect in 2022 for accurately predicting the races for governor and senator in Pennsylvania, even down to the margin of victory. The pre-election 2022 poll from Marist showed Governor Shapiro winning his race by 15 points, and Senator Fetterman winning his contest by five points. 

Mr. Shapiro would go on to be elected governor by a 14.8 percent margin, while Mr. Fetterman won his Senate seat by five points. 

The Marist poll released Thursday found a tighter race between Ms. Harris and Trump, with the vice president winning 50 percent of the vote and Trump at 49 percent.