Schiff, who led the House in its efforts to pass two articles of impeachment against Trump in December, spoke on the Senate floor for more than two hours.

He made lofty arguments about historical precedent, warning that if Trump is not removed, future presidents will feel free to seek foreign help with elections.

Trump was impeached over his efforts to pressure Ukraine President Volodymyr Zelenskiy to launch investigations into his political rival, former Vice President Joe Biden, and his son Hunter, along with a debunked conspiracy theory alleging Ukrainian interference in the 2016 presidential election.

While Trump sought those investigations, his administration was withholding hundreds of millions of dollars in military aid to Ukraine without providing a clear explanation. Democrats also impeached Trump for blocking the House's investigation into the matter, by refusing to hand over any documents and directing key witnesses not to comply with Congress.

Schiff began his remarks by tying the founding fathers' "prescient" views about impeachment to Trump through a quote from Alexander Hamilton:

"When a man unprincipled in private life desperate in his fortune, bold in his temper, possessed of considerable talents, having the advantage of military habits — despotic in his ordinary demeanour — known to have scoffed in private at the principles of liberty — when such a man is seen to mount the hobby horse of popularity — to join in the cry of danger to liberty — to take every opportunity of embarrassing the General Government & bringing it under suspicion — to flatter and fall in with all the non sense of the zealots of the day — It may justly be suspected that his object is to throw things into confusion that he may 'ride the storm and direct the whirlwind.'"

Schiff quickly moved to establish that Trump's dealings with Ukraine constituted abuses of the presidency – a preemptive strike against Trump's attorneys, who maintain that the president has done nothing wrong.

Trump, Schiff said, "does not, under our laws and under our constitution, have a right to use the powers of his office to corruptly solicit foreign aid, prohibited foreign aid, in his re-election."

"He does not have the right to withhold official presidential acts to secure that assistance, and he certainly does not have the right to undermine our elections and place our security at risk for his own personal benefit," Schiff said. "No president, Republican or Democrat, can be permitted to do that."

Schiff also employed the words of acting White House chief of staff Mick Mulvaney, who in October admitted – then tried to walk back – that the Ukraine aid was tied to investigations.

If this was allowed to stand, Schiff argued, there was no limit to the presidential malfeasance Americans would be told to just "get over it" in the future.

"Are we to accept, 'Well, the president says there was no quid pro quo, I guess that closes the case!'" Schiff asked rhetorically.

One of Trump's lead defense lawyers, Jay Sekulow, told reporters Wednesday that his team would "rebut" much of what Schiff alleged in his opening statement.

Their argument will be based on both "challenging the case that they made" and then making "an affirmative case" in Trump's defense, Sekulow said.

Sekulow singled out Democrats' implicit charge that Trump's decision to freeze the aid to Ukraine was directly tied to his request that Ukraine launch investigations into the Bidens.

"You noticed that Adam Schiff today talked about quid pro quo," said Sekulow, using the Latin term phrase meaning 'this for that' in reference to Schiff's remarks about Mulvaney.

"Notice what's not in the articles of impeachment – allegations or accusations of quid pro quo. That's because they didn't exist," Sekulow said.

The president's lawyers are expected to argue that Trump's decision first to withhold, and then abruptly release, nearly $400 million in aid to Ukraine last summer was unrelated to his request that Ukraine "do us a favor" by investigating the Bidens.

They are also expected to argue that the articles of impeachment against Trump themselves do not accuse the president of committing a crime under federal law.

Democrats fought for more than 12 hours Tuesday to ensure that the Republican-majority Senate would issue subpoenas for documents and witnesses, including Mulvaney and former national security advisor John Bolton.

But Schumer's 11 amendments to Senate Majority Leader Mitch McConnell's proposed rules were shot down, nearly all along party lines.

Over the next several hours, speculation grew on Capitol Hill that a possible deal could be struck whereby Bolton – who vowed that he would appear in the Senate if he was subpoenaed – could be allowed to testify if Hunter Biden was also brought in as a witness.

Democrats see Bolton as a key fact witness who was close to the president and the associates who were involved in the efforts toward Ukraine. Many Republicans have adopted Trump's suspicions about Hunter Biden, who served on the board of a Ukraine natural gas company while his father was vice president.

Schumer, however, poured cold water on the idea while speaking to reporters during a recess in proceedings Wednesday afternoon.

"No, I think that's off the table," Schumer said when asked about the possibility of a witness trade. "That trade is not on the table."

Wrapping up a trip to Davos, Switzerland to attend the World Economic Forum, Trump spoke to reporters about the impeachment, where he seemed to inadvertently admit that the White House refusal to turn over documents to Congress was helping his case.

"I got to watch enough — I thought our team did a very good job. But honestly, we have all the material. They don't have the material," he said.

House manager Val Demings, D-Fla., quickly seized upon Trump's remarks as an admission of guilt on the article of obstructing Congress.

Schiff also articulated how the seven Democratic House managers will spend the 24 hours – stretched out over three days, per the rules adopted in the wee hours Wednesday morning – that they have been allotted to make their case.

Schiff told the senators that his team will present evidence painting a "damning picture of the president's efforts to use the powers of his office to corruptly solicit foreign help in his re-election campaign and withhold official acts and military aid to compel that support."

Other members of the team took the helm after Schiff finished his first chunk of time. Nadler, followed by Texas Rep. Sylvia Garcia and Rep. Jason Crow of Colorado, then laid out a meticulous timeline of the entire Ukraine aid freeze. They relied heavily on video clips of the testimony of previous witnesses who appeared in the House impeachment inquiry.

Following the presentation of this evidence, which was still ongoing at 7:30 p.m. Wednesday night, Schiff said the next step would be for the managers to explain impeachment through a constitutional lens, and examine the necessary role of impeachment "as it was envisioned by the founders."

Finally, he said, Democrats would tie the previous two steps together, and "analyze how the facts of the president's misconduct and cover-up lead to the conclusion that the president undertook the sort of corrupt course of conduct that impeachment was intended to remedy."

Once the managers are done, Trump's lawyers then begin their defense. It's unclear if they plan to use the entire three-day window to state their case.