Washington (CNN) President Donald Trump's Senate trial will open in an atmosphere of acrimony Tuesday that will underscore how his impeachment, far from purging political corruption, is likely to tear even deeper national divides.

At a seminal moment of American history, 100 senators are serving as jurors and must decide whether to remove Trump from office for abusing power by leaning on Ukraine for personal political favors. They are already braced for an opening clash over the terms, shape and length of the trial.

Democrats are furious at Senate Majority Leader Mitch McConnell's plan for the trial, which will force House impeachment managers to deliver their case in two marathon 12-hour sessions that could stretch into the middle of the night. Trump's legal team will then have equal time to respond. The opening arguments are expected to begin Wednesday afternoon.

The blueprint could lead to the President being acquitted within a matter of days, which may also satisfy his demands for the trial to be over before he heads to Capitol Hill for his State of the Union address on February 4.

"It's clear Senator McConnell is hell-bent on making it much more difficult to get witnesses and documents and intent on rushing the trial through," Senate Minority Leader Chuck Schumer, D-New York, said on Monday evening.

"On something as important as impeachment, Senator McConnell's resolution is nothing short of a national disgrace. ... Senator McConnell's resolution stipulates that key facts be delivered in the wee hours of the night simply because he doesn't want the American people to hear them."

Schumer vowed to challenge the Kentucky Republican's plan with amendments on Tuesday at the start of the trial. Democrats are expected to try to force an early vote on the issue of calling new witnesses, a step that is provided for in McConnell's resolution at the end of the grueling process of prosecution and defense presentations.

The fact that McConnell's resolution includes language on potential votes over witnesses appears to be an attempt to navigate between Trump's demands for a swift acquittal and the desire of vulnerable swing-state Republican senators to avoid offering the impression that the trial is not fair.

Trump is facing two articles of impeachment, alleging abuse of power in Ukraine and obstruction of Congress, after he intervened to stop key officials from testifying to the House investigation before he was formally impeached in December.

The President was thousands of miles away from his trial Tuesday in Davos in the Swiss Alps, where he gave a speech touting America's success and his own new trade deals at the World Economic Forum. But he was still fuming about impeachment.

"It's just a hoax," he said when asked about the situation. "It's a witch hunt that's been going on for years, and frankly, it's disgraceful."

The trial is an emblem of wider political divides

The disputes over process at the start of only the third impeachment trial of a president reflect America's internal political estrangement, which has been exacerbated by a presidency built on exploiting societal fault lines.

Because everybody accepts that the President is almost certain to be acquitted, each smaller battle in the trial takes on extra political importance.

Democrats want to call new witnesses including former national security adviser John Bolton, who branded Trump's unofficial envoy to Ukraine, Rudy Giuliani, as a "hand grenade," and acting White House chief of staff Mick Mulvaney, who essentially confirmed a quid pro quo in Ukraine in public.

Democratic Sen. Ben Cardin of Maryland called for a process that allows testimony from key witnesses under oath.

"How can you have a fair trial if you don't hear from witnesses who have direct knowledge to the key facts?" Cardin said on CNN's "The Situation Room with Wolf Blitzer."

But Republicans are threatening to match such demands with subpoenas for former Vice President Joe Biden and his son Hunter -- despite the lack of any evidence that either was involved in corruption in Ukraine.

A new CNN/SSRS poll published Monday highlights the pressure on Republican senators -- such as Colorado's Cory Gardner, Maine's Susan Collins and Arizona's Martha McSally -- who face tough reelection races.

Sixty-nine percent of respondents said the trial should feature testimony from new witnesses who did not appear in the House impeachment hearings. The poll also explains the wider political dynamics around the trial.

About half of Americans -- 51% -- say Trump should be removed from office. But his approval rating remains at a steady 43%. The fact that only 8% of Republicans think Trump should be kicked out of the Oval Office helps explain why there is no two-thirds Senate majority to eject him.

There are already suspicions that McConnell's conditions for the prosecution and defense cases each to be presented in two 12-hour blocks are an attempt to hide the most damning allegations against Trump in late-night sittings.

Cardin suggested the plan may be designed to "saturate the hours so people don't pay attention and try to get this over quickly rather than allowing a fair trial to take place."

The dispute over witnesses who Democrats say are needed to ensure the trial offers a "fair" examination of Trump's alleged offenses is merely a symptom of the unbridgeable chasms between Republicans and Democrats.

In a sign that McConnell's rules will likely prevail, one moderate Republican, Sen. Lamar Alexander of Tennessee, said he would support them and pointed out that they did guarantee a vote on witnesses.

"Just because the House proceedings were a circus that doesn't mean the Senate's trial needs to be," Alexander said in a statement.

"We have a constitutional duty to hear the case. That means to me, No. 1, hear the arguments on both sides, and not dismiss the case out of hand. No. 2, ask our questions, consider the answers and study the record. No. 3, be guaranteed a right to vote on whether we need additional evidence. Evidence could be documents; it could be witnesses; or there could be no need for additional evidence," he said.

But there's no agreement even on basic facts: The rough transcript of a call that appears to show Trump leaning on Ukraine's President for dirt on Biden, Trump's potential 2020 rival, is touted by the President and his supporters as "perfect."

There's not even a common understanding of the meaning of impeachment itself. Trump's defense will be anchored on an argument that Congress' ultimate sanction against a president requires the commission of a crime.

But many scholars believe historical evidence shows the founders meant for the "high crimes and Misdemeanors" phrase in the Constitution to encompass abuses of the public trust by presidents using their power for personal gain.

In keeping with the tone of the Trump presidency, the White House defense brief released on Monday does not fully engage with the mountains of evidence suggesting troubling presidential conduct unearthed by the House impeachment inquiry.

It instead uses sloganeering and insults to blast the impeachment as a "charade" and claims that it is a "dangerous perversion" of the Constitution.

The clashes at the start of the trial also exemplify another dominant political theme of the era, of how a Senate Republican caucus that is ruthlessly competent in wielding power is in lockstep with a President who harbors an expansive vision of his own largely unrestrained authority.

At its root, the trial will raise a profound question about a core principle of American democracy -- whether the checks and balances that prevent one branch of government becoming too powerful are now unfit for that purpose.

Democrats reject Trump's defense

In a new pretrial brief filed on Monday, House Democratic impeachment managers pushed back on Trump's response to the Senate summons, in which his lawyers argued that he had acted within his rights in Ukraine.

"President Trump maintains that the Senate cannot remove him even if the House proves every claim in the Articles of impeachment. That is a chilling assertion," the nine-page brief said

"The Framers deliberately drafted a Constitution that allows the Senate to remove Presidents who, like President Trump, abuse their power to cheat in elections, betray our national security, and ignore checks and balances," the House managers wrote. "That President Trump believes otherwise, and insists he is free to engage in such conduct again, only highlights the continuing threat he poses to the Nation if allowed to remain in office."

"The Senate should speedily reject these deficient articles of impeachment and acquit the president," the brief said.

"The Articles themselves -- and the rigged process that brought them here -- are a brazenly political act by House Democrats that must be rejected," the 110-page brief argues

The President's lawyers also construct a new argument that he was well within his powers to ask Ukraine to investigate Biden.

"House Democrats' accusations rest on the false and dangerous premise that Vice President Biden somehow immunized his conduct (and his son's) from any scrutiny by declaring his run for the presidency," the lawyers write. "There is no such rule of law. It certainly was not a rule applied when President Trump was a candidate. His political opponents called for investigations against him and his children almost daily."

Such arguments are why many Democrats are wary of any step that could lead Hunter Biden to testify, as it could satisfy Trump's hope of dirtying the former vice president's image ahead of a possible November election duel.

Trump's claim that the impeachment is invalid because it does not charge a criminal offense is also a controversial position. It is expected to be laid out by veteran Harvard Professor Emeritus Alan Dershowitz.

Impeachment attorney and CNN legal analyst Ross Garber faulted the constitutional grounds for Dershowitz's argument.

"I'm not sure of anybody who defended more impeachments than I have. And even I think Dershowitz is wrong on this. I don't think you need a technical criminal violation for there to be an impeachable offense," Garber said.

CORRECTION: This story has been updated to accurately reflect Sen. Chuck Schumer's title as Senate Minority Leader.