In terms of the entire electorate, Biden still has a clear lead over President Donald Trump.

On average, recent opinion polls have measured support at 50.5 percent, compared to 43 percent for Trump, according to the policy site Realclearpolitics.

But the advantage has decreased since the end of June, when Biden led by 50.5 against 40.5 percent.

In addition, it is possible to get the most votes but still lose the election, which Hillary Clinton bitterly experienced in 2016. Then Trump won a majority of the states' electors, despite Clinton getting almost three million more votes.

Biden is losing ground in Florida

Much attention is therefore paid to the so-called "swing states" where the outcome is uncertain.

States like Florida and Ohio have many electors and can therefore be decisive for the outcome - as when the Republican George W Bush won the entire presidential election in 2000 thanks to a controversial victory with a few hundred votes in Florida. 

In Florida in particular, Biden has lost ground and now leads by just over a percentage point, according to Realclearpolitics.

Developments are about the same in North Carolina.

In Ohio, Trump has taken a narrow lead.

Smoother odds for players

Key states also include the traditionally democratic states of Pennsylvania, Michigan and Wisconsin, which unexpectedly supported Trump in 2016. Biden now has a clear but tight lead, 4-6 percentage points, according to Realclearpolitics.

The narrow gap between the candidates has also meant that the betting agencies pay almost as much dividend for a Trump victory as for a Bidens victory, according to current odds.

Just over a week ago, Trump was even considered the favorite of Betfair.

Weaker support among Latinos

Another bad sign for Biden is that support among Spanish speakers is lower than for the Democrats in the 2016 and 2018 elections. Clinton won by a margin of 38 percentage points, and in the 2018 by-elections, the Democrats won by 47 percentage points.

Now the measurements give Biden at best a lead of 32 percentage points, writes The New York Times.

A good sign for the party, however, is that Biden's lead nationally is significantly larger than Clinton's at the same time in 2016.