President Donald Trump vowed on Wednesday to fight all the way to the Supreme Court against any effort by congressional Democrats to impeach him, even though the US Constitution gives Congress complete authority over the impeachment process.

Trump’s threat, made in a morning tweet, came as the White House launched a fierce legal battle to fight subpoenas from Democrats in the House of Representatives for documents and testimony from his administration.

Democrats remain divided on whether to proceed with Trump’s impeachment after Special Counsel Robert Mueller’s Russia inquiry. Trump defiantly proclaimed on Twitter that the investigation “didn’t lay a glove on me”.

“If the partisan Dems ever tried to Impeach, I would first head to the US Supreme Court,” the Republican President, who is seeking re-election next year, said without offering details about what legal action he envisioned.

The Constitution gives the sole power of impeachment and removing a President from office to the House and the Senate, not the judiciary, as part of the founding document’s separation of powers among the three branches of the federal government.

House Speaker Nancy Pelosi and other Democratic leaders have remained cautious over launching impeachment proceedings against Trump ahead of the 2020 election, although they have left the door open to such action. Others in the party’s more liberal wing have demanded impeachment proceedings.

Mueller’s findings, released in a redacted report last week, detailed about a dozen episodes of potential obstruction of justice by Trump in trying to impede the inquiry but stopped short of concluding that he had committed a crime.

The report said Congress could address whether the President violated the law. Mueller separately found insufficient evidence that Trump’s campaign engaged in a criminal conspiracy with Russia in the 2016 presidential race.

Trump has ordered officials not to comply with subpoenas, and has filed a lawsuit to prevent material from being turned over to lawmakers. “We’re fighting all the subpoenas,” Trump told reporters at the White House on Wednesday. Under the Constitution, Congress is a co-equal branch of government alongside the executive branch and the judiciary.

The Constitution empowers Congress to remove a President from office for “treason, bribery or other high crimes and misdemeanours”. The House is given the power to impeach a President — bring formal charges — and the Senate then convenes a trial, with the senators as jurors, with a two-thirds vote needed to convict a President and remove him from office.