BLUE BELL, United States (AFP) — US President Joe Biden launched his harshest attack yet on Donald Trump as he kick-started his 2024 re-election campaign Friday, accusing the Republican of echoing Nazi Germany and posing a threat to democracy.

The 81-year-old Democrat branded his likely challenger in November a “loser” and “sick” in a speech on the eve of the third anniversary of the deadly January 6 Capitol attack by pro-Trump supporters.

“He’s willing to sacrifice our democracy, put himself in power,” Biden told supporters, alternating between whispers and furious shouts as he laid into the man he beat in 2020.

Not only had the twice-impeached former president instigated the Capitol attack, but the tycoon and his followers were still embracing “political violence” ahead of the 2024 vote, said Biden.

“He calls those who oppose him vermin. He talks about the blood of Americans being poisoned, echoing the same exact language used in Nazi Germany,” he added.

Biden chose a symbolic location for the speech near Valley Forge in Pennsylvania, the historic site where George Washington rallied American forces fighting their British colonial rulers nearly 250 years ago.

He portrayed himself as a defender of America’s institutions, warning that if Trump won a second term in the White House then democracy itself was at risk.

“Trump’s assault on democracy isn’t just part of his past. It’s what he’s promising for the future,” said Biden.

Biden’s full frontal attack on Trump came after criticism from some Democrats that the campaign has gotten off to a slow start.

Biden lags behind Trump in some polls, and also has the worst approval rating of any modern president at this stage in his term of office.

The president has failed to convince voters the economy is improving, while migration remains a headache and US support for Ukraine and Israel remains divisive among voters.

But perhaps Biden’s biggest vulnerability is his age: as America’s oldest-ever president, he has suffered a series of trips and verbal slips.

Biden, however, warned that the biggest issue of all was Trump, saying that “your freedom is on the ballot”.

“Today I make this sacred pledge to you that the defence, protection and preservation of American democracy will remain, as it has been, the central cause of my presidency.”

He accused Trump of being “sick” by laughing at a hammer attack on the husband of former US House Speaker Nancy Pelosi, and called him a “loser” over the 2020 election.

Biden also lashed out at Trump for his “love letters” to North Korean leader Kim Jong-un and his “admiration” for Russian President Vladimir Putin.

The Trump campaign swiftly hit back.

“Biden is the real threat to democracy by weaponising the Government to go after his main political opponent and interfering in the 2024 election,” Trump spokesman Steven Cheung told AFP.

The ex-president, himself on the campaign trail, added that Biden was “fear-mongering”.

“Biden’s record is an unbroken streak of weakness, incompetence, corruption and failure… That’s why Crooked Joe is staging a pathetic, fear-mongering campaign event in Pennsylvania today,” Trump told supporters in Sioux Center, Iowa.

Trump was impeached but acquitted over the January 6 riots. The 77-year-old now faces a criminal trial on charges of trying to subvert the 2020 election.