(CNN) A trio of legal scholars argued at the first House Judiciary Committee impeachment hearing Wednesday that President Donald Trump's unprecedented conduct was evidence of impeachable offenses, amid vocal protests and procedural roadblocks thrown up by Republicans to challenge the impeachment proceedings.

The opening impeachment hearing held by the panel expected to draft articles of impeachment was contentious from the moment Chairman Jerry Nadler gaveled it into session until he banged the hearing to a close to Republican protests more than eight hours later. Republicans repeatedly forced procedural votes and peppered Nadler with questions about what the committee was doing as they dismissed the entire proceeding as a sham.

The hearing marked an important step for Democrats in the impeachment proceedings, which have shifted from the House Intelligence Committee-led investigation to the Judiciary panel. Democrats are on track for an impeachment vote on the House floor by the end of the year, and House Speaker Nancy Pelosi held a closed-door, members-only meeting Wednesday morning where Democrats agreed to continue moving forward with the inquiry, asking her members: "Are you ready?"

The hearing was only the latest sign that all sides of the Capitol are preparing for an impeachment vote -- and a subsequent trial in the Senate. White House counsel Pat Cipollone was huddled with Senate Republicans at their party lunch Wednesday, while Vice President Mike Pence stopped by the House Republican conference meeting before the hearing. Senate Minority Leader Chuck Schumer, meanwhile, gave a presentation at his party's caucus lunch about the mechanics of a potential Senate trial.

And the Senate released its 2020 calendar on Wednesday -- leaving off the month of January, in anticipation of a trial.

The Judiciary Committee hearing provided new clues to the scope of the Democrats' expected articles of impeachment against Trump, with questions over obstruction of justice from former special counsel Robert Mueller's investigation suggesting there could be a Mueller element to the articles, in addition to charges related to Ukraine and obstruction of Congress.

Inside the hearing room, Democrats pushed past the Republican objections to elicit testimony from three of the four legal experts to explain why Trump's actions constituted impeachment offenses.

Those three professors, Harvard University's Noah Feldman , Stanford University's Pamela Karlan and the University of North Carolina's Michael Gerhardt , were all asked, based on the House Intelligence Committee evidence, "Did President Trump commit the impeachable high crime and misdemeanor of abuse of power?" All said that he did.

"If what we're talking about is not impeachable, then nothing is impeachable," Gerhardt said. "This is precisely the misconduct that the framers created a Constitution, including impeachment, to protect against."

While the three Democratic-invited law professors backed impeachment, the law professor called by Republicans to testify, George Washington University's Jonathan Turley , argued that Democrats were making a mistake by pursuing a "slipshod" impeachment that would have long-lasting consequences.

"I am concerned about lowering impeachment standards to fit a paucity of evidence and an abundance of anger. I believe this impeachment not only fails to satisfy the standard of past impeachments but would create a dangerous precedent for future impeachments," Turley said.

Nadler vowed to move swiftly to impeach Trump if his committee concludes that Trump committed impeachable offenses.

"Never before, in the history of the republic, have we been forced to consider the conduct of a president who appears to have solicited personal, political favors from a foreign government," said Nadler, a New York Democrat. "When we apply the Constitution to those facts, if it is true that President Trump has committed an impeachable offense — or impeachable offenses — then we must move swiftly to do our duty and charge him accordingly."

Republicans slammed the Democratic impeachment inquiry, which Rep. Doug Collins of Georgia, the top Republican on the committee, dismissed as a "railroad job."

"This is not an impeachment. This is simply a railroad job," Collins said. "And today is a waste of time."

In addition to the Ukraine allegations, Democrats have focused a portion of their questioning on the obstruction of justice allegations against Trump outlined in former special counsel Robert Mueller's report. Democrats haven't yet said whether the Mueller allegations will be included in potential articles of impeachment, as some congressional Democrats have pushed for.

As they questioned the academics, Democrats displayed a slide on a hearing room screen titled, "Impeachable offenses," which listed three items: "Abuse of power and bribery, obstruction of Congress, and obstruction of justice" — a possible hint about Democrats' intentions for articles of impeachment.

"How serious is that evidence of obstruction of justice?" Democratic counsel Norm Eisen asked Gerhardt.

"Obstruction of justice has been recognized as an impeachable offense both against President Clinton and President Nixon. This evidence that's been put forward by Mr. Mueller that's in the public record is very strong evidence of obstruction of justice," Gerhardt said.

Republicans force procedural votes

Republicans launched their protests of the hearing seconds after it began, which included forcing procedural votes on motions for House Intelligence Chairman Adam Schiff to testify, to have the whistleblower testify and to postpone Wednesday's hearing. The effort continued until the very end of the hearing, with Republican Rep. Louie Gohmert of Texas asking to be recognized to submit another item for the congressional record.

"Too late," Nadler said, banging the gavel down.

"Just typical," Gohmert responded as the witnesses began to exit.

The move from the Intelligence panel to the Judiciary Committee has ratcheted up the partisan temperature in the committee room, as the committee has some of the most vocal partisans in Congress on both sides of the aisle. But the law professors made clear they weren't going to just be props for a partisan fistfight.

Karlan pushed back against Collins, who said in his opening statement the professors "couldn't have possibly actually digested the Adam Schiff report from yesterday or the Republican response in any real way."

"Mr. Collins, I would like to say to you, sir, that I read transcripts of every one of the witnesses who appeared in the live hearing because I would not speak about these things without reviewing the facts, so I'm insulted by the suggestion that as a law professor I don't care about those facts," she said.

Later, Karlan and GOP Rep. Matt Gaetz of Florida got into a heated exchange, after Gaetz raised the political contributions and past writings of the law professors. He took aim at Karlan's joke earlier in the hearing that the President could name his son Barron but he could not "make him a baron."

"When you invoke the President's son's name here, when you try to make a little joke out of referencing Barron Trump, that does not lend credibility to your argument," Gaetz said. "It makes you look mean. It makes you look like you're attacking someone's family, the minor child of the President of the United States."

Karlan apologized for making the quip about Trump's son later in the hearing.

"I wish the President would apologize, obviously, for the things that he's done that's wrong, but I do regret having said that," Karlan said.

Republicans focused their questioning on Turley, giving him the opportunity to detail his problems with the Democratic impeachment inquiry. Turley argued that the Democrats have failed to provide evidence that meets "any reasonable interpretations" of the crimes they allege Trump has committed.

"If you are going to accuse a president of bribery, you need to make it stick, because you are trying to remove a duly elected president of the United States," Turley said. "The statement has been made not just by these witnesses but Chairman Schiff and others, that this is a clear case of bribery. It's not."

Turley also criticized the Democrats' accusation of obstruction of justice, saying that they have failed to let the courts rule on their subpoenas, unlike in the impeachment proceedings of Richard Nixon, by rushing the process.

"If you make a high crime and misdemeanor out of going to the courts, it is an abuse of power — it's your abuse of power," Turley said of Congress. "Fast and narrow is not a good recipe for impeachment."

Three 'impeachable offenses'

Democrats walked the law professors through the allegations that were detailed in the investigation led by the Intelligence Committee, which released its report on Ukraine and obstruction of Congress on Tuesday. Several clips of past witness testimony were played during the hearing to show how the President pushed Ukraine to investigate his political rivals and withheld a White House meeting and US security aid from Kiev.

"It wasn't just an abuse of power because the President was serving his own personal interests, but also an abuse of power insofar as the President was putting American national security interests behind his own personal interests," Harvard's Feldman said. "So it brought together two important aspects of the abuse of power: self-gain and undercutting our national security interests."

In addition to the Ukraine allegations, Democrats focused a portion of their questioning on the obstruction of justice accusations against Trump from the Mueller report -- which the Judiciary Committee was investigating in its own impeachment inquiry before the Ukraine scandal broke into the open in September and shifted the investigative focus to the Intelligence Committee.

Democrats haven't yet said whether the Mueller allegations will be included in potential articles of impeachment, as some congressional Democrats have pushed for. But the committee gave a possible hint about Democrats' intentions at the hearing, displaying a slide on a hearing room screen titled, "Impeachable offenses," which listed three items: "Abuse of power and bribery, obstruction of Congress, and obstruction of justice."

"How serious is that evidence of obstruction of justice?" Democratic committee counsel Norm Eisen asked Gerhardt.

"Obstruction of justice has been recognized as an impeachable offense both against President Clinton and President Nixon," Gerhardt said. "This evidence that's been put forward by Mr. Mueller that's in the public record is very strong evidence of obstruction of justice."

Judiciary Committee Democrats have yet to say what the next steps are in the inquiry, but Schiff said Tuesday that his staff would be presenting the Intelligence Committee report, which could be the next hearing the Judiciary panel holds.

Another question still unanswered is whether the President's attorneys will participate in the Judiciary Committee's impeachment proceedings. Trump's attorneys declined to participate in Wednesday's hearing, arguing that the process was unfair and they were given no details about the hearing itself.

Nadler has given the President's lawyers until Friday to say whether they will participate in future impeachment proceedings in the committee.

This story has been updated with additional developments Wednesday.