Clinton's lead in opinion polls fell from six percentage points to just three percentage points, and although many factors decided the very even election in 2016, many agree that the e-mail scandal had a real impact.
Following the revelation from the New York Post that a Ukrainian businessman thanked Joe Biden's son Hunter Biden for arranging a meeting with Joe Biden, the Trump campaign hopes to see a similar effect as in the election campaign four years ago.
Biden has previously said that he never discusses his son's foreign affairs with this one, and President Trump has now repeatedly called Joe Biden corrupt and relaunched the accusation he gave Hillary Clinton in 2016 - "crooked Joe Biden".
Fewer voters are uncertain
But it is far from obvious that Trump will see the same effect as four years ago.
The information since 2016 was straightforward and clear, and also came directly from the FBI.
The revelation from the New York Post is snarky, and does not prove that there has actually been any meeting between Biden and the Ukrainian businessman, or what a possible meeting played or led to.
The information in the computer has also reached the journalists via a third party - President Trump's personal lawyer Rudy Giuliani increases the risk that the Americans see the revelation as a party submission.
Fewer voters have also said that they are unsure of who to choose before this election compared to the previous one.
In addition, over 35 million Americans have already voted in the election.
This corresponds to about 25 percent of all votes cast in 2016. Among them are voters that Trump certainly would have liked to attract.
Tough uphill
The election campaign has recently become increasingly dirty with attacks in both directions.
Joe Biden has called the president a clown, a racist and a threat to US democracy.
President Trump has called Biden criminal, weak and stupid.
It is still possible that there will be more surprises and revelations.
If they become more concrete and compromising for Joe Biden, rather than for his son, a lot can still happen.
But President Trump has continued a tough uphill climb if he is to succeed in turning public opinion around.