Former Vice President Joe Biden has been privately telling people that he may launch a bid to run for the Democratic presidential nomination if no Democrat emerges who could beat Trump.

"If someone emerges that the former VP believes can beat [Trump], I think he is at peace with that," a Biden donor told Politico. "On the other hand, if that person doesn’t exist or doesn’t run, you can expect Joe Biden to take a very serious look."

If Biden chooses to run, it would be the sixth time he's seriously considered or launched a presidential campaign.

Biden will be 77 years old by 2020 but will have decades of experience in government that many younger Democrats will lack.

Biden is about to hit the road for his "Promise Me, Dad," book tour. The memoir was written in honor of his late son, Beau Biden, who died in May 2015, an event that Biden says kept him from running for the nomination.

However, Biden is in high demand as a politician whose name can go a long way for novices. His office receives an average of five requests for endorsements or event attendances each week, one person with knowledge of his schedule said.