In a pre-trial brief - Trump's first comprehensive defense - the president's legal team, led by White House counsel Pat Cipollone and Trump private attorney Jay Sekulow, argued the president did nothing wrong and said: "The Senate should speedily reject these deficient articles of impeachment and acquit the president."
Trump is charged with abusing the powers of his office by pressuring Ukraine to investigate his political rival, Joe Biden, and obstructing a congressional probe into his conduct.
Trump's lawyers asserted that the abuse of power charge was not an impeachable offense, saying "House Democrats' newly-invented 'abuse of power' theory collapses at the threshold because it fails to allege any violation of law whatsoever."
The pre-trial brief also rejected the obstruction of Congress charge as "frivolous and dangerous," saying the president exercised his legal rights by resisting congressional subpoenas and that finding otherwise "would do lasting damage to the separation of powers."
The president's lawyers also accused House Democrats of conducting a rigged process and argued, as Trump and his allies have repeatedly, that this was an effort to overturn Trump's 2016 election victory.
The Republican-controlled Senate is highly unlikely to remove Trump from office, but the president has sought to diminish the accusations from Democrats as a partisan witch-hunt, as he seeks to limit the political damage to his re-election bid.
Trump on Monday also sought to show he is still conducting presidential business despite the trial, scheduling a trip to Davos, Switzerland, where he'll join global leaders at the World Economic Forum. Some advisers had argued against him making the trip.