Donald Trump has mounted an all-out assault on the election result in Michigan, reportedly planning to fly state lawmakers to meet with him in Washington and phoning county officials in an apparent attempt to derail the certification of Democrat Joe Biden’s 150,000-vote victory in the state.

On Tuesday night, Trump placed phone calls to two Republican members of a county-level vote certification board the night before the pair tried to reverse their previous endorsement of a large chunk of the vote in Michigan.

The news emerged as Republican lawmakers in Michigan prepared to fly to Washington on Friday to meet with Trump at his request, the Washington Post first reported.

While no explanation for the meeting has been given, Trump has been pressuring Republican state lawmakers to try to hijack the electoral college by advancing slates of electors that could compete with those selected by the states’ voters.

There was no indication that Trump’s strategy, which in addition to the consent of legislatures would require a string of highly unlikely court victories and ultimately participation by Democrats in Congress to succeed, had any remote chance of overturning the election.

But Trump’s full-court press in Michigan has raised concerns about the integrity of the state’s election result, which has an election certification deadline of Monday 23 November.

As members of the Wayne county board of canvassers, William Hartmann and Monica Palmer played a crucial role this week in transforming Michigan’s popular vote into all-important electoral college votes for Biden. Michigan has 16 electoral votes.

But at a meeting on Tuesday night, Hartmann and Palmer at first refused to certify the vote in Wayne county, which hosts the city of Detroit and where more than 80% of the vote is African American, citing minor irregularities. Biden won the county by more than 330,000 votes – his largest margin of any county in Michigan.

After three hours of discussion among community members attending the meeting virtually, some of whom accused Hartmann and Palmer of carrying out a brazen, racist assault on the right to vote, the pair certified the Wayne county vote. In the past the process has been treated as routine.

Trump spoke with Palmer on the phone later that night, she told the Detroit Free Press. “He was checking to make sure I was safe,” she said. Palmer said that she and her family had “received multiple threats”.

The next day both Hartmann and Palmer filed affidavits in court seeking to reverse their certification of the Wayne county result, claiming that they had been promised internally that the vote would be audited, only to discover it would not be.

The White House did not reply to a request for comment. Neither did Hartmann or Palmer. Trump inaccurately tweeted on Tuesday night that the board had declined to certify the Wayne county vote, indicating that he was following the process closely.

The Michigan secretary of state, Jocelyn Benson, said through a spokesperson on Thursday that the certification was final. “There is no legal mechanism for them to rescind their vote,” she said. “Their job is done and the next step in the process is for the board of state canvassers to meet and certify.”

The vice-chairman of the Wayne county board of canvassers, Democrat Jonathan Kinloch, denied the substance of the affidavits, telling the Washington Post that the Republican pair understood the process and knew what they were certifying.

Ever since Trump’s election loss two weeks ago, the Trump campaign has been filing lawsuits and applying pressure on Republican officials in multiple states in an effort to overturn the election result or, barring that, to spread the false belief that Biden’s victory was illegitimate. Polling indicates that they are succeeding in the latter objective with a majority of Republicans.

Trump campaign tampering had not caused a serious hitch in the process of vote certification, however, until Tuesday night.

Biden needs electoral votes to make his win over Trump official, although he defeated Trump in a sufficient number of states that he still would win in the electoral college even if the Trump campaign managed to steal the election in multiple big states such as Michigan and Pennsylvania.

Separately in Michigan on Thursday, the Trump campaign withdrew an election-related lawsuit in federal court, making the false assertion in court documents that the Wayne county vote had not been certified. The Trump lawyer Rudy Giuliani was leading that case.

The Trump campaign’s legal strategy came under question in a separate case in Pennsylvania, where on Wednesday the campaign proposed that the campaign itself should conduct a review of mail-in ballots and let the court know what it found. As of this writing the court had not taken up the offer from the campaign, which has failed to advance any of its dozens of lawsuits since election night.