When it comes to Donald Trump, there are certain signs that can't be mistaken. By insisting, on September 11, that his debate with Kamala Harris the previous day had been "rigged," the former president effectively admitted that he had not exactly shone in the face of the solid performance given by the Democratic presidential candidate. The vice president's appearance had been eagerly awaited, and she didn't disappoint her camp.

After approaching her opponent in the opening moments of the debate to force him into a handshake he had not anticipated, she skilfully played on Trump's inflated ego to draw him into the pitfalls in which he has invariably become entangled, whether it be the quality of his campaign rallies or his fascination with dictators.

In doing so, Harris continued down the path to a spectacular political transformation. Joe Biden's decision to withdraw from the presidential race on July 21, after a disastrous debate with Trump, has in less than eight weeks transformed a somewhat fallible vice president, of mediocre popularity, into a candidate adored by the Democratic camp, capable of rallying huge crowds seduced by a pro-active, forward-looking discourse.

The September 10 debate also demonstrated, however, that this transformation is still incomplete. The rushed and highly unusual conditions of her nomination did not allow Harris to develop the carefully considered political plan, traditionally polished during primaries, that would give her candidacy its full weight. Her reluctance to answer questions – she has only granted one interview since the president stepped down from the race – leaves those about her objectives and the means to achieve them unanswered.

The undecided

First and foremost her responses to the issues voters are most concerned by – the economy, even if inflation is currently falling, and immigration, a challenge facing many Western governments – which are often deemed insufficient. Nor has Harris tackled another challenge head-on: that of linking her candidacy to the administration she has been part of for more than three and a half years, whose record has been harshly judged by American voters.

After a successful start to the campaign, a unifying nomination convention and a successful first debate, Harris needs to go further to maintain, and above all strengthen, the momentum behind her. A successful debate in September is no guarantee of success in November, as Hillary Clinton found out to her cost in 2016, and polling data confirms that the presidential race remains particularly uncertain in the key states.

Until now, the Democrat has played a virtuoso role in relieving her camp after the withdrawal of Biden, who was heading for an inevitable defeat due to his age and physical limitations. She now has to convince the few undecided voters, in a country deeply divided in two, that she is the person best equipped to respond to their concerns. She still needs to flesh out what a Harris presidency might look like.