Elizabeth Warren has struck back at Donald Trump on her first day campaigning for president, saying she is not certain that the president will even still be in office on election day in 2020 — or even out of jail.

Ms Warren, a senator from Massachusetts, made the suggestion during a campaign rally in Iowa on Sunday, where she called the president out for what she described as “racist” behaviour and rhetoric.

“By the time we get to 2020, Donald Trump may not even be president,” Ms Warren said at an event in Cedar Rapids. “In fact, he may not even be a free person.”

Ms Warren is among a handful of Democratic candidates who have declared their candidacy for president this year, having officially launched her run on Saturday in her home state. In doing so, she joined what is expected to become one of the largest fields of candidates in recent memory.

The senator, who has frequently sparred with Mr Trump, recently became the focus of his ire after reports surfaced from decades ago in which she claimed Native American heritage.

Ms Warren released DNA test results last year showing she had genes consistent with having distant Native American relatives. The testing rollout stirred up controversy, and Ms Warren apologised afterwards for equating DNA to cultural ancestry and traditions.

The president and his supporters have since latched onto the testing debacle to decry Ms Warren as racially insensitive, but she showed on Sunday that she has no intention of pulling her punches on the issue.

“There’s a racist tweet, a hateful tweet. Something really dark and ugly,” Ms Warren said, describing what she says is a regular occurrence for the president. “And what are we, as candidates, as activists, the press, going to do about it?”