Washington (CNN) - House Democrats are hours from crossing a somber point of no political return as they get set to roll out articles of impeachment Tuesday accusing President Donald Trump of abusing power and obstructing Congress.

The momentous step toward making Trump only the third president to be formally impeached in nearly two-and-a-half centuries of US history comes in a tumultuous third year of his term and only 11 months before the next general election.

"This is not a happy day," said House Foreign Affairs Committee Chairman Eliot Engel, one of several key Democratic leaders expected to make a formal announcement on Tuesday morning. "But I think we are doing what we have to do."

Democrats have accused the President of abusing his power by withholding nearly $400 million in US military aid to Ukraine and the prospect of a visit to the Oval Office by new President Volodymyr Zelensky in order to coerce the former Soviet state into investigating potential 2020 foe Joe Biden. Such conduct, they say, is worthy of impeachment because it amounts to bribery, puts Trump's own political goals ahead of America's national interests and effectively invited a foreign power to interfere in a US election.

"The scheme by President Trump was so brazen, so clear, supported by documents, actions, sworn testimony, uncontradicted contemporaneous records that it's hard to imagine that anybody could dispute those acts, let alone argue that that conduct does not constitute an impeachable offense or offenses," said Barry Berke, presenting the case against Trump for the Democrats in a Judiciary Committee hearing on Monday.

Republicans have struggled to counter the facts laid out by witnesses drawn from ranks of foreign policy and military officers. But they deny Trump did anything wrong at all, let alone anything that reaches the level of impeachment.

"It's a disgrace. A hoax," the President said at the White House on Monday, without bothering to counter any of the evidence.

The top Republican on the House Judiciary Committee, Rep. Doug Collins of Georgia, meanwhile accused House Speaker Nancy Pelosi of rushing to impeachment -- with expectations that Democrats will hold a full House vote on the issue next week.

"The speaker of the House after hearing one day of testimony in the Judiciary Committee, said, 'Go write articles.' Facts be damned," Collins said.

Full story at https://edition.cnn.com/2019/12/10/politics/donald-trump-impeachment/index.html