Joe Biden and Donald Trump

Joe Biden's all-out attack on Donald Trump in his first 2024 campaign speech said it all — the US president knows he is in for the fight of his political life.

The 81-year-old Democrat has the worst approval ratings of any modern president at this stage in his term, and is either neck-and-neck or trailing his likely Republican opponent in the polls.

For months Democrats have been clamoring for Biden's campaign to step up to the plate, as voter concerns mount about the economy and the age of America's oldest president.

Biden did just that on Friday. He launched into a ferocious condemnation of Trump, comparing his rival to the Nazis and branding him "sick," a "loser" and a threat to US democracy.

The question now is whether that strategy — identifying Trump as his main rival even before the Republican nomination process officially starts in Iowa later this month — will be enough.

"If the election were held tomorrow, President Biden would lose," William Galston, senior fellow at the Brookings Institution, told AFP.

‘Uphill fight’

Until now Biden's strategy has focused on positive messages about the president's accomplishments -- particularly on leading the economy out of the Covid-19 pandemic.

But "they haven't really moved the needle so far," said Galston, particularly as many Americans are still feeling the effects of high food and housing prices, whatever the improving government statistics say.

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Migration through the Mexican border remains a major headache, while there is division in his party over his support for Israel's war on Hamas, and Republicans in Congress are blocking his bid for more funds for Ukraine.

Another major worry is that Biden has been hemorrhaging support among the Black and Hispanic voters who helped him to the White House in 2020.

But perhaps Biden's biggest vulnerability is his age: he has suffered a series of trips and verbal slips that Trump, just four years younger at 77, has repeatedly mocked.

Galston said Biden would have to wage a "vigorous campaign," including multiple trips to battleground states and presidential debates, to convince voters he was not "doddering and senile."

"If he can't wage a vigorous campaign I'm afraid that will simply validate the doubts," he said.

On the economy, Biden would be reliant on wages continuing to rise faster than prices, and a lack of shocks such as a wider Middle East war.

"My overall thesis is that President Biden's campaign is going to have to hope that global events and the domestic economy cooperate," he said.

"Otherwise, that's going to be an uphill fight for the election."

Agence France-Presse