The U.S. House of Representatives is plunging into a landmark impeachment week, with Democrats who once hoped to sway Republicans now facing the prospect of an ever-hardening partisan split over the historic question of removing President Donald Trump from office.

Lawmakers were getting their first look Monday night — behind closed doors — at the impeachment report from the House intelligence committee. The report, to be released Tuesday, is expected to forcefully make the Democrats' case that Trump engaged in what chairman Adam Schiff calls impeachable "wrongdoing and misconduct" in withholding military aid while pressuring Ukraine to investigate Democrats and Joe Biden while.

For Republicans, the proceedings are simply a "hoax," with Trump insisting he did nothing wrong and his party allies in line behind him. Late Monday, he tweeted his daily complaints about it all and then added a suggestive question: "Can we go to Supreme Court to stop?"

He didn't elaborate.

It's all boiling down to a historic test of political judgment in a case that is dividing Congress and the country.

Departing Monday for a NATO meeting in London, Trump criticized the timing of the impeachment inquiry hearing, which will occur while he is out of the country.

Speaking to reporters at the White House, Trump said the NATO trip is "one of the most important journeys we make as president" and the summit date was established a year ago.

He said Republicans are united in opposing impeachment and the inquiry is backfiring on Democrats, adding, "I think it is going to be a tremendous boost for the Republicans."

Heading to Europe to represent our Country and fight hard for the American People while the Do Nothing Democrats purposely scheduled an Impeachment Hoax hearing on the same date as NATO. Not nice! <a href="https://t.co/LCXYhoOWF6">pic.twitter.com/LCXYhoOWF6</a> —@realDonaldTrump

For the Democrats, House Speaker Nancy Pelosi faces a critical test of her leadership as she steers the process ahead after resisting the impeachment inquiry through the summer, warning it was too divisive for the country and required bipartisan support.

Speaking to reporters at the international climate conference in Madrid, Pelosi declined to engage with impeachment questions. "When we travel abroad, we don't talk about the president in a negative way," she said. "We save that for home."

Hearings set for Wednesday

Possible articles of impeachment are focused on whether Trump abused his office as he pressed Ukrainian President Volodymyr Zelensky in a July 25 phone call to launch investigations into Trump's political rivals. At the time, Trump was withholding $400 million US in military aid, jeopardizing key support as Ukraine faced an aggressive Russia at its border.

The report from the intelligence panel also was expected to include material the Democrats say suggests obstruction of Congress, based on Trump's instructions for his administration to defy subpoenas for documents and testimony.

The next step comes Wednesday, when the judiciary committee gavels its own hearings open ahead of a possible impeachment vote by the full House by Christmas. That would presumably send the issue to the Senate for a trial in January.

The Democratic majority on the intelligence committee says its report, compiled after weeks of testimony from current and former diplomats and administration officials, will speak for itself in laying out the president's actions toward Ukraine.

Republican rebuttal

Ahead of the report's public release, Republicans pre-empted with their own 123-page rebuttal.

In it, they claim there's no evidence Trump pressured Zelensky. Instead, they say Democrats just want to undo the 2016 election. Republicans dismiss witness testimony of a shadow diplomacy being run by Trump lawyer Rudy Giuliani, and they rely on the president's insistence that he was merely concerned about "corruption" in Ukraine — though the White House transcript of Trump's phone call with Zelensky never mentions the word.

"They are trying to impeach President Trump because some unelected bureaucrats chafed at an elected president's 'outside the beltway' approach to diplomacy," according to the report from Republicans Devin Nunes of California, Jim Jordan of Ohio and Michael McCaul of Texas.

Trump on Monday pointed to Zelensky's recent comments as proof he did nothing wrong. The Ukrainian president said in an interview he never talked to Trump "from the position of a quid pro quo," but he didn't say Trump did nothing wrong. In fact, he had strong criticism for Trump's actions in the Time magazine interview.

With Ukraine at war with Russia, he said, its partners "can't go blocking anything for us."

Swift timeline

The finished intelligence committee report sets up the week's cascading actions. The panel is expected to vote to send the findings to the judiciary committee, which will take the lead on considering articles of impeachment.

As the process intensifies, judiciary on Wednesday will convene legal experts whose testimony, alongside the report, will begin to lay the groundwork for possible charges.

Democrats could begin drafting articles of impeachment against the president in a matter of days, with voting in the judiciary committee next week.

Republicans on the committee, led by Rep. Doug Collins of Georgia, plan to rely on procedural moves to stall the process and portray the inquiry as a sham.

The White House declined an invitation to participate, with counsel Pat Cipollone denouncing the proceedings as a "baseless and highly partisan inquiry" in a letter to judiciary chairman Jerrold Nadler, Democrat from New York.

Trump had previously suggested that he might be willing to offer written testimony under certain conditions, though aides suggested they did not anticipate Democrats would ever agree to them.

Cipollone's letter of nonparticipation applied only to the Wednesday hearing, and he demanded more information from Democrats on how they intended to conduct further hearings before Trump would decide whether to participate.

Nadler said Monday if the president really thought his call with Ukraine was "perfect," as he repeatedly says, he would "provide exculpatory information that refutes the overwhelming evidence of his abuse of power." House rules provide the president and his attorneys the right to cross-examine witnesses and review evidence before the committee, but little ability to bring forward witnesses of their own.

Asked why not have his lawyers participate, Trump said Monday: "Because the whole thing is a hoax. Everybody knows it."