Joe Biden warned that Trump was a national security threat and called himself the interim president

US President Joe Biden warned in an interview aired on Sunday that Trump "poses a real threat to American security".

In an interview with CBS News, Biden said, "Mark my words, if he wins... This election, see what happens."

"He poses a real threat to American security. Look, we are at a turning point in world history... Democracy is the key."

Biden decided to drop out of the presidential race after a poor debate performance with Trump on June 27.

In this television interview, he appeared weak but determined. He again admitted he had lost the debate, but stressed there were "no serious problems" with his health.

"For me, a key issue remains the preservation of democracy in the country. I have an obligation to the country to do the most important thing we can do, and that is, we must, we must, we must defeat Donald Trump."

Democratic hopes of victory have soared since Joe Biden withdrew from the US presidential race. Harris' approval ratings have been rising, while Trump has struggled.

Biden said he was expected to serve only one term when he won in 2020, but was persuaded to stay on.

"I consider myself a transitional president. I can't even tell you how old I am. It's hard for me to say this, but things moved so fast that it didn't happen."