A new survey shows a significant swing toward Vice President Harris, when compared to President Biden’s popularity, with notable shifts among independents and younger voters.

The poll from Emerson College found that Ms. Harris now leads President Trump 50 percent to 46 percent nationally. In the last survey from Emerson in early July, Trump led Mr. Biden 46 percent to 43 percent.

With the undecided voters in the survey allocated based on their leanings, Ms. Harris also leads Trump nationally, 48 percent to 42 percent. Ms. Harris maintains a 48 percent to 44 percent margin when attorney Robert Kennedy Jr.’s support is accounted for as well.

The survey of 1,000 likely voters has a margin of error of plus or minus three points.

Ms. Harris’s lead over Trump is built on increases in support among specific groups, such as independent voters, among whom Ms. Harris is now leading Trump by 46 percent to 45 percent. Ms. Harris is also leading among voters under 30.

“Likely voters under 30 have shifted toward Harris by nine points, 56 percent of whom supported Biden, 65 percent now support Harris,” a pollster, Spencer Kimball, said. “Voters over 70 also support Harris over Trump, 51 percent to 48 percent — last month they broke 50 percent to 48 percent for Trump.”

While some voter groups have shifted in favor of Ms. Harris, she has also improved voter enthusiasm among reliably Democratic voting blocs, like Black women.

“While the overall share of likely voters motivated to vote had little movement, Black voters who say they are ‘extremely’ or ‘very’ motivated to vote this November increased 11 points, from 80 percent to 91 percent,” Mr. Kimball said.

Ms. Harris is also now viewed favorably by a majority of voters, 51 percent, while Trump is viewed favorably by 45 percent of voters. 

In the generic congressional ballot, Democrats have seen an increase of support of two points, and they now lead Republicans 48 percent to 46 percent.