Will Donald Trump's old rival Elizabeth Warren run against him for president in 2020?

Massachusetts senator Elizabeth Warren is being mooted for a possible 2020 presidential run after she announced plans to join the Armed Services Committee in 2017.

The Democrat, who has a long-running and well-publicised feud with Donald Trump, said the decision was spurred on by the presence of her three brothers in the military, although it has fuelled speculation she is preparing for a presidential bid.

Lawrence O'Donnell of MSNBC called Warren's decision to join the committee as a "very important move that could be a first step in a presidential campaign."

However, Warren has claimed a 2020 run is not on her "radar screen" in an interview with a Massachusetts TV channel, in which she was asked whether she would consider a future presidential bid, to which she responded: "Oh, come on".

Warren was reportedly a favourite of some liberals to run as a candidate in 2016, a suggestion she did not pursue, instead throwing her weight behind Hillary Clinton. She was at one point rumoured to be under consideration for Clinton's VP pick, prior to her choosing Tim Kaine.

A 2020 run could potentially pit her against long-term adversary Trump, if indeed he were to run for a second term and Warren were chosen as her party's presidential nominee.

The pair has an ongoing Twitter feud, with Trump accused of racism after mocking Warren's Native American ancestry and referring to her as "Pocahontas".

Although Trump has not yet commented on Warren's potential 2020 run, the rumour has already prompted criticism from America Rising Squared, the group that opposes liberal politics, although it has also been met with support from other corners.

"America's military men and women deserve better than Warren using the Armed Services Committee as yet another platform for her all-but-announced 2020 presidential campaign," Jeremy Adler, a spokesman for America Rising Squared, which is an offshoot of super PAC America Rising, told The Hill.