Democratic presidential candidate Kamala Harris has said that if she wins the White House, her justice department “would have no choice” but to pursue an obstruction of justice case against President Donald Trump after he leaves office.

The California senator and some other Democrats in the 2020 race are pushing their party to initiate the impeachment process in the wake of special counsel Robert Mueller’s report on Russian interference in the 2016 election.

Mr Mueller has said he was unable to exonerate Mr Trump of obstruction but could not pursue potential charges because of a Justice Department policy that bars the indictment of a sitting president, a policy Ms Harris has said she would ask her justice department to re-examine.

“Everyone should be held accountable,” Ms Harris told NPR in an interview that aired on Wednesday.

“And the president is not above the law.”

Ms Harris, a former California attorney general who also was San Francisco’s district attorney, later said she would not dictate the outcome of any prospective efforts to charge Mr Trump.

“The facts and the evidence will take the process where it leads,” she said.

Suggesting that Mr Trump face prosecution after he leaves office is a fine line for any Democrat after the party has excoriating him for politicising the Justice Department.

Impeachment remains popular with Democrats’ base voters, but the party’s congressional leaders are more cautious because the Republican-controlled Senate does not likely have the votes to remove Mr Trump from office.

Mr Harris is not alone among 2020 Democratic presidential hopefuls in criticising the Justice Department policy that Mr Mueller cited in declining to look at obstruction charges in his nearly two-year investigation of Mr Trump.

Massachusetts Senator Elizabeth Warren, the first candidate to fully endorse the start of impeachment proceedings in the wake of Mr Mueller’s report, pledged last month to end that policy if she is elected president.

Ms Harris and Ms Warren are among nearly one-half of their party’s 20-plus primary field in calling for the start of an impeachment inquiry, though few contenders are making that stance a centrepiece of their campaigns.

But Ms Harris, who is running in part on the strength of her legal and law enforcement experience, appears to have taken a step further than her opponents in affirming that a Justice Department in her administration “should” look at charging Mr Trump with obstruction once he no longer is president.

President Donald Trump (Patrick Semansky/AP)

“I do believe that we should believe Bob Mueller when he tells us, essentially, that the only reason an indictment was not returned” was because of the current policy that bars indictment of a president while in office, Ms Harris told NPR.

“But I’ve seen prosecution of cases on much less evidence.”

Eric Columbus, who served as a justice department and department of homeland security lawyer during the Obama administration, suggested recently on Twitter that any Democratic candidate asked about seeking charges against Trump answer by promising, “unlike the current president,” not to “interfere with” the impartial administration of justice.

The statute of limitation for seeking obstruction charges, as in most federal criminal cases, is five years from the time an alleged crime is committed.

The time limit for charges in conspiracy cases begins at the time of the last act in an alleged conspiracy.