Donald Trump’s lawyers and Democrats arguing for his removal from office clashed on Tuesday over the powers of his office, as the president’s legal team echoed his allegations about the House investigation that led to his impeachment.

House Intelligence Committee chairman Adam Schiff used his lengthy opening statement to warn senators to resist transforming Mr Trump into “a monarch” by allowing him to set the terms of a trial that will determine whether he is ousted from the Oval Office.

But White House counsel Pat Cipollone responded on the first day of Mr Trump’s impeachment trial by alleging that House Democrats put forth “fraudulent” evidence and “have no case.”

The president and his legal team spent the historic day – he is only the third sitting US chief executive to face a Senate impeachment trial – trying to discredit the evidence gathered by House Democrats during the investigation late last year that ended with a mostly party line vote to impeach him on counts of abusing his power and obstructing Congress.

For months, Mr Trump described the House probe as a shady “hoax” held in the bottom floor of the Capitol, eager to plant seeds of doubts in the minds of the few voting blocs that will determine whether he wins a second term in November. Mr Cipollone, for instance, hit House Democrats for holding their investigation “in secret."

Both sides used ample parts of their opening statements to debate whether witnesses should be called during the upper chamber’s proceeding. Mr Trump has said he would invoke executive privilege to block the testimony of current and former White House aides, including acting chief of staff Mick Mulvaney and former National Security Adviser John Bolton.

Mr Bolton has said he would testify if issued a subpoena. One of his former aides, Fiona Hill, told House lawmakers during a public impeachment hearing last year that Mr Bolton once referred to what Mr Mulvaney and US ambassador to the European Union Gordon Sondland wanted from the Ukraine government as a “drug deal”.

All the president's lawyers: The team fighting Trump's impeachment Show all 6 1 /6 All the president's lawyers: The team fighting Trump's impeachment All the president's lawyers: The team fighting Trump's impeachment Alan Dershowitz Dershowitz is a controversial American lawyer best known for the high-profile clients he has successfully defended. Those clients have included OJ Simpson, Jeffrey Epstein and Harvey Weinstein. One longtime Harvard Law associated told the New Yorker Dershowitz "revels in taking positions that ultimately are not just controversial but pretty close to indefensible." Getty All the president's lawyers: The team fighting Trump's impeachment Ken Starr Starr became a household name in the 1990s as the independent counsel who led the investigation that led to Bill Clinton's impeachment. That investigation began as a look into a real estate scandal known as Whitewater, and eventually led to impeachment after Mr Clinton lied under oath about having an affair with White House intern Monica Lewinsky. AP All the president's lawyers: The team fighting Trump's impeachment Jay Sekulow Sekulow is the president's longtime personal attorney, and, now, personal lawyer in the White House. He has been accused by former Rudy Giuliani associate Lev Parnas of being "in the loop" during the Ukraine scandal. Getty All the president's lawyers: The team fighting Trump's impeachment Pam Bondi Bondi is the former attorney general in Florida, and a longtime backer of the president's. She made a name for herself in Florida for taking hyper partisan stances on issues, and her penchant for publicity. She is likely to be a prominent public-facing figure during the trial. AFP/Getty All the president's lawyers: The team fighting Trump's impeachment Pat Cipollone Cipollone is the White House counsel, and leading the president's defence team. Getty All the president's lawyers: The team fighting Trump's impeachment Rudy Giuliani While not officially named as one of the president's impeachment lawyers, it is hard to ignore Giuliani's outsized role in this process. The former mayor of New York has been making headlines for months as he defends his client, and for his apparent role in the effort to compel Ukraine to launch the investigation into Joe Biden. We'll see how he figures in the actual trial, which he has said he would like to be a part of. Reuters

Jay Sekulow, one of the president’s attorneys, continued team Trump’s argument that the House Democratic impeachment managers, if senators side with them and oust the 45th president, would essentially be eroding the constitution. He said that was because the office of the president’s “assertion of privilege is backed by decades of precedent.”

Mr Sekulow sounded a lot like Mr Trump when he contended that House Democrats opted to impeach the president because they remain offended that he was elected three years ago.

“Why are we here? Are we here because of a phone call or are we here before this great body because since the president was sworn into office there was a desire to see him removed?” Mr Sekulow said, calling the impeachment probe “re-insurance” and an “umbrella policy” after the Russia election meddling probe led by former Special Counsel Robert Mueller failed to bring down Mr Trump’s presidency.

Using executive privilege has been “utilised by presidents since the founding” of the country,” Mr Sekulow said, adding it exists to “protect the constitution and the separation of powers.”

Trump's lawyer Pat Cipollone tells Senate trial that president has done nothing wrong

But in no way did Mr Trump's attorneys parrot their boss more than in the top White House lawyer’s contention about November’s presidential election.

“They’re not here to steal one election, they’re here to steal two elections,” said Mr Cipollone in one of his first public statements since becoming the White House’s top attorney.

But Mr Schiff argued the opposite, saying the president’s “conduct … would have alarmed the founders.”

Senate majority leader Mitch McConnell has said he is working in lock step with the White House’s legal team. Mr Schiff alluded to Mr Trump’s influence over the chamber’s rules for the proceeding, saying it would mean any commander in chief “cannot be indicted, cannot be impeached.”

Adam Schiff throws Trump's own words back at him

“It makes him a monarch,” the California Democrat said as senators sat silent in accordance with the chamber’s guidelines for an impeachment trial.

Earlier, Mr McConnell, under pressure, made several changes to the trial rules he penned and Democrats had sharply criticised.

Opening arguments will still span 48 hours – 24 for each side – but ould now last up to three days rather than being jammed into just two. The Kentucky Republican also changed course by altering his rules resolution to automatically include the entire package of evidence the House used to impeach Mr Trump into his chamber's trial.

Minority leader Chuck Schumer had said initial rules drawn up by Mr McConnell "seem to be designed by Trump, for Trump" and would have forced "presentations to take place at two or three in the morning so the American public can't see them."

In the evening the chamber rejected, on party line votes, a pair of amendments offered by Senate Minority Leader Chuck Schumer calling for subpoenas of White House and State Department documents. A third Schumer amendment on the same matter was also expected to be defeated on Tuesday night.

For his part, White House aides with Trump at the World Economic Forum in Davos, Switzerland, said he is receiving regular briefings about the goings-on on the Senate floor. Shortly after leaving a working dinner at that forum, the president sounded a now-familiar refrain.

“READ THE TRANSCRIPTS!” he tweeted, referring to a White House-prepared summary of his July 25 telephone call with Ukraine’s president in which Democrats say he linked investigations of US Democrats to a massive military aide package Kiev expected in its continued standoff with Russia and its larger and more sophisticated military. The line is part of the Trump side’s argument that he broke no laws and did nothing wrong.

Robert Bauer, a New York University School of Law professor and a former White House counsel under President Barack Obama, calls that contention “mistaken.”

“The federal campaign finance law bars soliciting anything of ‘value’ from a foreign national to influence a federal, state and local election,” he wrote on the Lawfare blog. “Whether the solicitation was made and ‘value’ received depends on the facts – facts with which Alan Dershowitz claims he has no intention of engaging.”