With all eyes on Donald Trump's bid to lead Republicans back into the White House, U.S. President Joe Biden's re-election push has slipped under the radar in an unusual start to his campaign.

After a dispute with officials in New Hampshire over scheduling, he will not be on the ballot when the state's primary kicks off the party's nomination process on Tuesday.

The quarrel threatens to leave the president in a theoretical third place among Democrat candidates, behind little-known gelato magnate Dean Phillips and low-polling self-help author Marianne Williamson.