Only 38% of poll respondents said they approved of Biden's performance as president, down from 40% in December.

His public approval rating has held below 50% since August 2021, stirring concern among his fellow Democrats as he faces an expected election rematch with Republican former President Donald Trump in November. A separate Reuters/Ipsos poll earlier this month showed Trump with a six percentage-point lead in that matchup.

The latest poll found rising concern about immigration, with 17% of respondents listing it as the most important problem facing the U.S. today, up sharply from 11% who cited as the most pressing issue in December. It was the top concern of Republican respondents, with 36% citing it as their main worry, above the 29% who cited the economy.

Biden's administration has struggled to cope with a surge of asylum seekers on the U.S.-Mexico border, while Republicans in Congress, egged on by Trump, have threatened to scuttle a bipartisan attempt to tackle the problem. They are pressing ahead with an effort to impeach Biden's top border official, Homeland Security Secretary Alejandro Majorkas.

U.S. border authorities struggled in December to process migrants as apprehensions reached nearly 11,000 in a single day, which officials said was near or at a record high.

The economy remained Americans' overall top concern, cited by 22% of poll respondents, as they have struggled with inflation and other aftershocks of the COVID-19 pandemic.

Nearly two-thirds of respondents, including 47% of Democrats, said the country was on the wrong track.

The online poll of 1,019 U.S. adults was conducted Friday through Sunday. It has a margin of error of plus or minus 3.3 percentage points for all respondents, 6.4 points for just Republicans and 6.1 points for just Democrats.

(Reporting by Andy Sullivan; Editing by Scott Malone and Jonathan Oatis)

By Andy Sullivan