Democrat U.S. presidential candidate Joe Biden maintains a nine-point lead over President Donald Trump after their combative first debate, according to a 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 percent of likely voters were backing Biden, while 41 percent said they were voting for Trump. Four percent said they were voting for a third-party candidate and five percent were not sure. 

Biden has held the same nine-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.

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

Among those who are expected to cast ballots in the upcoming election, 51 percent said they planned to vote before the election, either by mail or in person at early voting locations, and six percent 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 U.S. adults, including 830 likely voters. It has a credibility interval, a measure of precision, of about four percentage points.

Trump suggested on Thursday that he won't agree to any rule changes at the remaining two debates with Biden. 
  
"Why would I allow the Debate Commission to change the rules for the second and third Debates when I easily won last time?" Trump tweeted, while several polls showed that most viewers think Biden did better in the first 2020 presidential debate.

The tweet came a day after the Commission on Presidential Debates said it's considering changes to the format of the next two debates to "ensure a more orderly discussion of the issues" amid wide criticism that the first Trump-Biden matchup was messy and unpresidential. 
  
On the stage in Cleveland, Ohio on Tuesday night, Trump interrupted Biden on nearly every topic he was talking about and mocked his intellect and performance in college, while the former U.S. vice president hit back by calling his opponent a "liar" and a "clown" and asked him to "shut up." 

The second debate will be held on October 15 at Adrienne Arsht Center for the Performing Arts in Miami, Florida, Trump's home state and a battleground for this year's presidential election. Belmont University in Nashville, Tennessee, will host the third and the last Trump-Biden debate on October 22. 
  
There will also be a vice presidential debate between Vice President Mike Pence and Biden's running mate, U.S. Senator from California Kamala Harris, at the University of Utah in Salt Lake City, on October 7. 

(With input from Reuters, Xinhua)