Joe Biden's 9-point lead stable after presidential debate: Reuters/Ipsos poll

Democrat Joe Biden maintains a 9-point lead over President Donald Trump after their combative first debate, according to Reuters/Ipsos polling that shows most Americans have settled on their choice for president little more than a month before the November 3 election.

The most recent survey, conducted Tuesday through Thursday, found that 50% of likely voters were backing Biden, while 41% said they were voting for Trump. Four percent said they were voting for a third-party candidate and 5% were not sure.

Biden has held the same 9-point advantage in six of the past seven national polls dating back to early September.

The polling indicates that Biden remains an early favorite to win the national popular vote. To win the election, however, a candidate must prevail in enough states to win the Electoral College, and state polls show that Trump is nearly as popular as Biden in many battleground states.

Read: Will you shut up, man? Biden tells Trump after interruptions by the President

Biden has led Trump in most national surveys all year, and his edge among likely voters has not changed despite a number of developments with the potential to shake up the presidential race.

The former vice president's lead remained the same after the death of US Supreme Court Justice Ruth Bader Ginsburg last month gave Trump an opportunity to nominate her successor and solidify the court's conservative majority. Biden's margin also did not change after the New York Times reported on the weekend that Trump frequently paid no federal income taxes in the 15 years leading up to his presidency.

View: Highlights from the first US presidential debate 2020: Top quotes by Donald Trump and Joe Biden

The unruly presidential debate on Tuesday in which Trump repeatedly interrupted Biden and the moderator and questioned his rival's intelligence, while Biden called the president a racist and a liar, also did not move the needle.

Eighty-seven percent of likely voters said they were now "completely certain" about their choice for president, according to the poll. Only about 13%, including 10% of likely Democratic voters and 15% of likely Republican voters, appeared to be wavering in their choice.

Among those who are expected to cast ballots in the upcoming election, 51% said they planned to vote before the election, either by mail or in person at early voting locations, and 6% said they had already voted.

The Reuters/Ipsos public opinion poll was conducted online, in English, throughout the United States. It gathered responses from 1,314 US adults, including 830 likely voters. It has a credibility interval, a measure of precision, of about 4 percentage points.