US President Joe Biden has been trying to calm the fears of Democrats nervous about his chances in the November election. He wrote a letter on Monday to Democratic lawmakers in Congress, saying he is "firmly committed" to beating his rival, Donald Trump.

Lawmakers and donors saw Biden struggle to express himself in a debate with Trump about two weeks ago. Many are raising concerns about his health, and more of them have come out to say he should withdraw.

Biden acknowledged in his letter that he is not "blind" to the worries voters have about "what is at stake." He says he knows "better than anyone" the responsibilities of the nominee. He added that Democrats spoke clearly during the primaries and chose him by a "wide margin."

Biden touted his successes during more than three years in the White House. He says he has created more than 15 million new jobs, revitalized manufacturing and lowered the costs of healthcare.

He says Americans should never allow Trump anywhere near the Oval Office again. He added that the riot on the Capitol on January 6, 2021 proves his predecessor is "unfit" to serve.

US media report multiple lawmakers have approached the House Minority Leader, Hakeem Jeffries, calling for the president to step aside. However, others want Jeffries to bring members into line.

Biden wants lawmakers in his party to "end" their calls for him to drop out of the race. He says they must move forward as a "unified" party because any weakening of resolve "only helps Trump."