JUST IN: Biden demands Dems unify around him to ‘defeat Donald Trump’

Biden wrote in the caption of the post with the letter, “This morning, I sent a letter to my fellow Democrats on Capitol Hill. In it, I shared my thoughts about this moment in our campaign. It’s time to come together, move forward as a unified party, and defeat Donald Trump.”

The letter stated, "Now that you have returned from the July 4th recess, I want you to know that despite all the speculation in the press and elsewhere, I am firmly committed to staying in this race, to running this race to the end, and to beating Donald Trump."

"I have had extensive conversations with the leadership of the party, elected officials, rank and file members, and most importantly, Democratic voters over these past 10 days or so. I have heard the concerns that people have - their good faith fears and worries about what is at stake in this election," Biden added.

Later in the letter, Biden added that he has "no doubt" that he and the Democrats "can and will beat Donald Trump." Biden claimed his "historic record of success" as evidence that he and the party can run on in order to run against Trump in the upcoming election.

Biden ended the letter stating, "The question of how to move forward has been well-aired for over a week now. And it's time for it to end. We have one job. And that is to beat Donald Trump. We have 42 days to the Democratic Convention and 119 days to the general election. Any weakening of resolve or lack of clarity about the task ahead only helps Trump and hurts us. It is time to come together, move forward as a unified party, and defeat Donald Trump."

This comes amid growing concerns over Biden's age and mental capacity, which have been mounting among congressional Democrats as well as others in the party after his dismal debate performance against Donald Trump in June. Many pundits and donors have weighed in to say that they believe Biden should leave the race and allow a younger Democrat to run.