Former vice-president Joe Biden has announced he will seek the presidency, becoming the most prominent name to enter the crowded field of Democratic candidates competing to take on Donald Trump in the 2020 election.

“The core values of this nation … our standing in the world … our very democracy … everything that has made America America is at stake. That’s why today I’m announcing my candidacy for President of the United States,” Biden tweeted.

His decision to enter the race marks his third presidential campaign – after two unsuccessful attempts at earning the Democratic nomination in 1988 and 2008 – and puts to rest months’ of speculation over his intentions to make a last run for the White House.

Bolstered by his legacy as Barack Obama’s vice-president, Biden was expected to be an early frontrunner in a diverse Democratic field that features several heavyweight contenders but no clear favorite.

Biden, 76, joins a diverse crop of candidates that includes four senators: Elizabeth Warren of Massachusetts, Kamala Harris of California, Kirsten Gillibrand of New York, and Cory Booker of New Jersey — as well as Hawaii Representative Tulsi Gabbard and Julian Castro, the former mayor of San Antonio and housing secretary under Obama.

If successful, Biden would become the oldest person to be elected president in US history.

But allegations from several women that they were left feeling uncomfortable by their physical interactions with Biden has left created some uncertainty over the former vice-president’s prospects.

While Biden has not been accused of sexual assault or harassment, a mounting list of women have came forward to complain that he violated their personal space.

The allegations prompted renewed scrutiny of what had long been dismissed as Biden’s affectionate posture and raised fresh questions over his viability as a candidate in the #MeToo era.

The controversy started with Lucy Flores, a former Nevada state assemblywoman who claimed in an op-ed that Biden placed his hands on her shoulders, leaned in to smell her hair and kissed the back of her forehead at a political event in 2014. Other women subsequently came forward with similar stories, prompting an apology from Biden, who pledged in a video to adjust his behavior.