WASHINGTON 

US President Joe Biden said Wednesday that his predecessor, Republican presidential candidate Donald Trump, poses a threat to American democracy. 

Addressing reporters one day after he formally announced his reelection campaign, Biden said he knows Trump "well" and he understands "the danger he presents to our democracy."

"We've been down this road before," Biden said at the White House, maintaining "I still would be running if he wasn't."

Biden officially joined Trump, who was the first person from either party to announce a 2024 presidential run, in the White House race Tuesday. While Biden is widely expected to receive his party's nomination, Trump's path to the Republican ticket faces far more hurdles with a growing group of fellow partisans vying for the bod.

A member of the Democratic Party, Biden served 36 years in the US Senate and eight as vice president under President Barack Obama. Already the oldest president in US history, Biden would be 86 at the end of a second term, raising questions among many about his capacity to hold America's highest office.

Previously, Ronald Reagan was the oldest American president. He ended his second term at the age of 77 and was diagnosed with Alzheimer's disease five years after he left office.

On Election Day 2024, former President Donald Trump will be 78 -- the same age Biden was when he was first elected president.

While Biden's announcement marked the formal start of his campaign, he has spent months going around the country to tout his legislative victories, including a historic infrastructure revitalization bill, new funding to boost high-technology manufacturing and climate initiatives.

But Trump insisted in a lengthy statement that if you were to gather the "five worst presidents in American history, and put them together" they would not "have done the damage Joe Biden has done to our Nation in just a few short years. Not even close."

"American families are being decimated by the worst inflation in half a century. Banks are failing. Our currency is crashing and the dollar will soon no longer be the world standard," he said. "And Joe Biden has led us to the very brink of World War III."

Off the campaign trail, Trump is facing four criminal probes, including in Georgia, where prosecutors are examining whether he and his political allies sought to illegally change the outcome of the state's 2020 presidential election results, and a pair of federal investigations related to Trump's actions concerning the Jan. 6, 2021 Capitol insurrection and his handling of classified documents after he left office.

The prosecutor leading the Georgia probe announced Monday she would announce whether to bring any criminal charges as early as July.