United States President Donald Trump's legal team asserted Monday that he did "absolutely nothing wrong", calling the impeachment case against him "flimsy" and a "dangerous perversion of the Constitution".

The brief from Trump's lawyers, filed before arguments expected this week in the Senate impeachment trial, offered the most detailed glimpse of the lines of defence they intend to use against Democratic efforts to convict the president and oust him from office over his dealings with Ukraine. It is meant as a counter to a brief filed two days ago by House Democrats that summarised weeks of testimony from more than a dozen witnesses in laying out the impeachment case.

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The 110-page filing from the White House shifted the tone towards a more legal response. Still, it hinged on Trump's assertion that he did nothing wrong and did not commit a crime - even though impeachment does not depend on a material violation of law but rather on the more vague definition of "other high crimes and misdemeanors" as established in the US Constitution.

The filing says the two articles of impeachment brought against the president - abuse of power and obstruction of Congress - don't amount to impeachment offences. It asserts that the impeachment inquiry centred on Trump's request that Ukraine's president open an investigation into Democratic rival Joe Biden was never about finding the truth.

"Instead, House Democrats were determined from the outset to find some way - any way - to corrupt the extraordinary power of impeachment for use as a political tool to overturn the result of the 2016 election and to interfere in the 2020 election," Trump's legal team wrote. "All of that is a dangerous perversion of the Constitution that the Senate should swiftly and roundly condemn."

The prosecution team of House managers was expected to spend another day on Capitol Hill preparing for the trial, which will be under heavy security. Before the filing, House prosecutors arrived on Capitol Hill to tour the Senate chamber. Opening arguments are expected within days following a debate over rules.

The White House brief argues that the articles of impeachment passed by the House are "structurally deficient" because they charge multiple acts, creating "a menu of options" as possible grounds for conviction.

The Trump team claims that the Constitution requires that senators agree "on the specific basis for conviction" and that there is no way to ensure that the senators agree on which acts are worthy of removal.

The team accused Democrats of diluting the standards for impeachment, an argument that echoed the case made Sunday by one of Trump's attorneys, Alan Dershowitz, who contended in talk shows that impeachable offences must be "criminal-like conduct". That assertion has been rejected by scholars, and Representative Adam Schiff, the Democratic chairman of the House Intelligence Committee, called it an "absurdist position".