WASHINGTON • The first wave of long-promised negative ads from the Trump campaign began this week in caustic form, flooding Facebook pages and television screens in swing states, with harsh messages that make unfounded inferences about Mr Joe Biden's mental state and paint the presumptive Democratic presidential nominee as too friendly towards the Chinese government.

This month alone, the Trump campaign has spent or reserved about US$7 million (S$10 million) on television airtime in local markets, fuelling negative ads that repeat xenophobic tropes regarding the Chinese origin of the coronavirus and unearth positive comments Mr Biden has made about China in the past.

The campaign's ads on Facebook have taken their own dark turn. Videos on the platform declare "Geriatric Health is No Laughing Matter" or "Joe Biden: Old and Out of It", then use selective edits of Mr Biden's verbal stumbles and meandering soliloquies to make less-than-subtle suggestions about his mental acuity.

The negative ad offensive, backed by a budget considered significant for this stage of the campaign, represents a turning point in the general election. Though President Donald Trump often takes to his Twitter account to skewer Mr Biden as tired and boring, his campaign's expansive digital advertising operation has been almost exclusively focused on raising money and finding new donors online.

Last week, the Trump campaign boasted it was about to "press fire" on a dormant arsenal of data-driven digital and TV ads. It plans to spend US$10 million on its opening salvo against Mr Biden, a budget first reported by Politico.

As of late last month, the campaign and the Republican National Committee had a US$187 million cash advantage over Mr Biden and the Democrats.

By pummelling Mr Biden on China and mental fitness, the Trump campaign is trying to define him early in the election race, at a time when many Americans, stuck at home amid the Covid-19 crisis, are even more tuned in to glowing screens, big and small.

The new ads that focus on China have two lines of attack. One criticises Mr Biden for saying the President's decision to restrict travel from China because of the coronavirus outbreak was "hysterical xenophobia".

But most of the ads simply highlight statements that Mr Biden made when he was vice-president, like "China is not our enemy".

Mr Trump, too, has at times praised China and its President Xi Jinping, occasionally undermining attempts by aides and his campaign to portray China as the villain responsible for the virus.

The Trump campaign is suddenly moving to play catch-up after Democratic groups aligned with Mr Biden have taken to the airwaves to attack Mr Trump, including over his performance in responding to the coronavirus. Two groups, Priorities USA and American Bridge, have spent at least US$20 million on anti-Trump ads since March 1.

Mr Trump's campaign has been frustrated with its own aligned super PAC (political action committee), America First, for not doing more on television during this period of time.

Indeed, the last incumbent president to run for re-election - Mr Barack Obama in 2012 - benefited from an aggressive super PAC. At the time, Mr Obama's campaign and his allies aired constant negative ads against Mr Mitt Romney, largely with the help of their supportive super PAC.

Professor Ken Goldstein, a professor of politics at the University of San Francisco, said: "If this election is about Trump, he probably loses. Trump's only hope is to make the election about Biden."

The Trump and Biden campaigns did not immediately respond to requests for comment on Thursday.

"All of those ads that they put out - what they're doing is testing those to see which resonate best with different sorts of people," Prof Goldstein said.

"And then whichever ones that work best on Facebook, then first, you'll see more of them on Facebook. Then they'll fire for effect onto television."

NYTIMES