President Donald Trump: Photo by Evan Vucci/AP/Shutterstock

The White House will not cooperate with the impeachment inquiry in the US House of Representatives, calling it constitutionally illegitimate and accusing Democrats of engaging in political theatre.

In a letter to the lawmakers on Tuesday, the White House called for them to abandon the inquiry, claiming they are seeking to overturn the results of the 2016 election, which President Donald Trump won.

House Democrats in September launched the probe amid accusations Trump used his power as president to try to have Ukraine dig up dirt on his domestic political rival, Joe Biden, and aid his upcoming re-election campaign.

US public opinion is split on the issue.

The Democratic speaker of the House, Nancy Pelosi, called the White House’s refusal to cooperate unlawful in a statement responding to the letter, which she said is manifestly wrong.

The move to not comply with any requests for testimony or documents was described by a senior administration official as a full halt on cooperation.

This sets up a stalemate between the executive and legislative branches, which likely will see the courts being asked to decide on specific issues.

President Trump and his Administration cannot participate in your partisan and unconstitutional inquiry under these circumstances,the White House said to Democrats.

Pelosi said the latest move by the Republican president was an effort to stonewall Democrats’ investigations, claiming they had evidence that Trump abused his office.

The White House alleged lawmakers were violating Trump’s due-process rights in the inquiry, including the right to issue subpoenas and question witnesses.

Moreover, the executive branch dismissed the legitimacy of the investigation, saying there was no full vote in the House on starting the inquiry.

Democrats do not believe such a vote is necessary, as Congress is constitutionally vested with oversight of the White House.

There is also an argument that the president will have full due process rights if the Democratic controlled House impeaches and the Senate then holds a trial.

The letter from the White House to Democrats came hours after Trump’s administration blocked Gordon Sondland, the US ambassador to the European Union, from testifying to lawmakers.

In justifying his move, Trump called the House of Representatives a kangaroo court.

Sondland featured in text messages between US diplomats released last week, which show at least one senior official alarmed by Trump’s behaviour towards Ukraine, worried he was using the power of his office to gain a political edge.

Adam Schiff, a Democrat leading the House investigations, said he believes there is important information on Sondland’s electronic device, which is being held by the State Department.

He said this showed the need to be able to get documents from the administration.

The president, in the days since the scandal erupted, openly called for Ukraine and China to investigate his rival and his son, Hunter Biden.

The younger Biden received a cushy salary and job on the board of a Ukrainian energy company, while his father was a key government figure working on Ukraine.

There is no evidence they did anything illegal, but the appearance of a conflict of interest is haunting the family.

Trump says he did not nothing wrong in a call with Ukrainian President, Volodymyr Zelensky in July.

A reproduced transcript of the call, released by the administration, shows Trump asking for a favour from Zelensky and bringing up investigations into Biden.

Trump surrogates push his line that there was no quid pro quo with Zelensky, though this argument does not deal directly with the accusation that the president was seeking dirt on his political rival from a foreign government.

There is also concern Trump was withholding military aid to Ukraine as part of his efforts.

The decision by the White House to stop any cooperation is not without political risk for the Republicans. Democrats may charge they are carrying out a cover-up.

Outspoken Republicans have said the process is too flawed to warrant cooperation and will not be fair to the president.

Trump continues to enjoy broad support within his own centre-right party.