Donald Trump has said he “very easily” answered written questions from special counsel Robert Mueller, although he speculated that the questions had been “tricked up” to try to catch him in a lie.

“They’re all done,” the president told reporters at the White House on Saturday before leaving for California, adding that his responses will soon be submitted to Mr Mueller’s team.

“We do that next week,” he said, in what signals a new phase of the inquiry.

In a swipe at the investigation into 2016 election interference and possible ties between Moscow and the Trump campaign, the president said earlier that “you have to always be careful when you answer questions with people that probably have bad intentions”.

Mr Mueller has signalled a willingness to accept written answers on matters related to collusion with Russia. Mr Trump’s lawyer Rudy Giuliani has said repeatedly the president would not answer Mr Mueller’s questions on possible obstruction of justice.

During months of negotiations with the special counsel office, Mr Trump’s lawyers have repeatedly counselled the president against sitting down for an in-person interview.

Mr Mueller’s year-and-a-half-long investigation has produced guilty pleas and convictions from several top Trump aides even as the special counsel and the White House have engaged in lengthy negotiations about how — or if — the president would give evidence.

Though he spent hours with his lawyers, Mr Trump on Friday insisted: “My lawyers don’t write answers, I write answers.”

The president’s remarks were fresh evidence of his return to the ominous rhythms of the Russia probe after spending weeks enjoying adulation at campaign rallies before the midterm elections.

Despite his insistence that he is “very happy” with how things are going, his frustrations with the probe have been evident everywhere from his Twitter feed this past week to his private grousing that the special counsel may target his family.

There is also the criticism he is getting over his choice for acting attorney general, as well as late-arriving election results that have largely been tipping towards House Democrats.

“The inner workings of the Mueller investigation are a total mess,” Mr Trump tweeted on Thursday. The investigators do not care “how many lives they can ruin”, he wrote.

A day later, he tried to put a rosier shine on the situation, telling reporters: “I’m sure it will be just fine.”

The president continued to maintain his innocence while launching new broadsides.

After a relative lull in the run-up to the midterms, the Russia probe has returned to the forefront of Washington conversation. There has been widespread media coverage of two Trump allies — Roger Stone and Jerome Corsi — who say they expect to be charged.

The president has expressed concerns behind closed doors that Mr Mueller is closing in on his inner circle, including potentially his eldest son.

For months, the president has told confidants he fears Donald Trump Jr, perhaps inadvertently, broke the law by being untruthful with investigators after a June 2016 Trump Tower meeting with a Kremlin-connected lawyer, according to one Republican close to the White House.

Mr Trump has also complained about efforts in the Senate by his long-time foe, senator Jeff Flake, to introduce legislation to protect the special counsel, according to the officials and Republicans.

Additionally, Mr Trump has told confidants in recent days that he is deeply frustrated by widespread criticism of his choice of Matthew Whitaker for acting attorney general, according to officials.

Mr Whitaker has been a vocal opponent of the special counsel probe.