Democrats warned to keep euphoria in check as election remains on knife-edge

Strategists fear that feelgood factor around Kamala Harris risks underestimating scale of challenge in swing states

• Democratic national convention – follow live

Anxious Democratic strategists are quietly trying to douse the euphoria engulfing Kamala Harris’s presidential campaign by warning that her surge in popularity masks an election contest that is on a knife-edge and could easily be lost.

As the vice-president basks in adulation and optimism at the Democratic national convention in Chicago, key supporters are cautioning that more trying times lie ahead after an extended honeymoon period following her ascent to the top of the ticket in place of Joe Biden.