Biden hits 79 as potential successors watch from wings

As Joe Biden pops the cork on his alcohol-free birthday bubbly this weekend, he will not need to be reminded that he was born as close to the end of Abraham Lincoln's presidency as he was to the start of his own.

The veteran Democrat, who turns 79 on Saturday (Nov 20), has said publicly that he intends to run for re-election, but there has been persistent speculation that he could change his mind given his advanced years.

There is usually little intrigue around the nomination when a United States president is still in his first term, as no occupant of the White House has declined to seek re-election since Lyndon Johnson more than 50 years ago.

But Biden would be 86 at the end of a second term, and potential successors and their sponsors are already circling, seeing another four years as an assignment too far in Biden's storied political career.

In a new Politico/Morning Consult poll, only 40 per cent of voters surveyed agreed with the statement that Biden "is in good health", while 50 per cent disagreed - a 29-point shift over a year.

"If his health declines, as sometimes happens in one's 80s, his plans might change," said David Greenberg, a journalism and history professor at Rutgers University in New Jersey.

"That would create a wide-open field, with many of the 2020 runners-up as possibilities, as well as a lot of people who didn't run."

If Biden were to become the nation's first octogenarian presidential candidate, he would be somewhat undermining the status he gave himself during the campaign as a "bridge" to the next generation - taken by many as a tacit assurance that he would not seek a second term.

History-making Kamala Harris - the first woman and first black and Asian American ever sworn in as vice president - would be the heir apparent.