Texas Attorney General Ken Paxton "wasn't the man he publicly proclaimed to be," the state House Republican who is leading the impeachment case against Paxton told the state Senate on Tuesday.

"He betrayed his constituents and the sacred public trust that's been given him. And in Texas, we require more from our public officials than to merely avoid being a criminal," state Rep. Andrew Murr said in his opening statement as Paxton's impeachment trial began Tuesday afternoon.

He said witnesses in the Senate's trial, which will play out over the next two or three weeks, "will provide the clarity the Senate needs, and the public deserves, to find out what was really happening behind closed doors."

Murr's comments came after Paxton, through his attorney Tony Buzbee, pleaded not guilty to 16 articles of impeachment that are up for consideration during his Senate trial.

The trial started after the Senate voted to reject motions from Paxton's team to dismiss the impeachment case in its entirety, and to dismiss individual articles of impeachment. Twelve Republicans joined all 12 Democrats in voting 24-6 to continue the trial. The GOP-led Senate also voted 22-8 against a motion to exclude all evidence before January 2023.

Lt. Gov. Dan Patrick, a longtime Paxton ally who is presiding over the Senate's trial, said Paxton cannot be compelled to testify during the proceedings -- describing the process as similar to a criminal trial.

Paxton was present through the day's opening hours to enter his not guilty plea. But he was not on hand Tuesday afternoon during opening statements.

Buzbee, one of his attorney, insisted that there is "nothing to this," and said allegations that Paxton had abused his office to benefit friend and donor Nate Paul were "based on ignorance, innuendo and outright lies."

"Ken Paxton gave nothing of significance to Nate Paul. Nate Paul received nothing of significance from Ken Paxton. This whole case is a whole lot of nothing," Buzbee said.

He added: "I do wonder, are we really going to get a fair trial here? Have you already decided based on what's politically expedient or what's best for you personally? Or is it even possible to get a fair hearing?"

The opening statements kicked off the Senate's consideration of Paxton's impeachment by the Texas House, which voted 121-23 in May to impeach Paxton after he requested $3.3 million in state funds for a settlement with former staffers who had accused him of abusing his office to benefit Paul.

Paxton is a firebrand conservative who has aligned himself with former President Donald Trump. Following the 2020 election, he sued in a failed effort to overturn Trump's loss to Joe Biden, seeking to have the electoral college votes of four swing states won by Biden thrown out. He has so far survived a series of scandals since taking office in 2015, though he remains under indictment in a separate securities fraud case.

He has described his impeachment as a "politically motivated sham" and has consistently denied wrongdoing.

In 2020, top Paxton aides published a letter accusing the attorney general of abuse of office, bribery and improper influence -- complaints centered on Paxton's ties to donor and friend Nate Paul.

Four of the former staffers later sued the attorney general's office, claiming they were fired in violation of the state's whistleblower law. In February, Paxton agreed to a settlement in which he did not admit fault and the whistleblowers would be paid $3.3 million. He asked state lawmakers to fund that settlement.

The House impeachment managers have already submitted nearly 4,000 pages of evidence, unveiling more details in the extraordinary accusations that Paxton pressured his top aides to take steps that would benefit Paul, a real estate investor.

Paxton is accused of accepting $20,000 in countertop materials from Paul through a contractor during a remodeling of his home.

Also included in the allegations is that Paxton had a mistress, whom Paul hired as a favor to the attorney general, and that Paxton would use an alias -- "Dave P" -- on Uber to meet up with the mistress, as well as Paul.

Paul was arrested in June on eight federal felony charges related to falsifying financial records, and his lawyer has repeatedly declined comment to CNN.

Trial could last two or three weeks

There are 19 Republicans in the 31-member Texas Senate. One of them is Paxton's wife, Angela Paxton, but she is not eligible to vote at the trial.

If the 21 of the remaining 30 eligible senators vote to convict Paxton, he would become the third person ever removed from office in Texas via impeachment proceedings.

The trial is expected to last two or three weeks. It is taking place in the Texas Senate chamber, with some observers filing in to watch early Tuesday morning.

Mark and Cindi Montgomery of New Braunfels began lining up at the Capitol doors before daylight so they could get passes to sit in the gallery and show their support for Paxton.

"It's a sham impeachment," said Mark Montgomery. "He was elected by the people."

Cindi Montgomery said they booked their hotel in Austin months ago, as soon as they learned the trial date.

Mark Montgomery said he was aware of Paxton's securities fraud indictment and the other allegations against him when he voted to reelect Paxton last year.

"He's standing up for Texas," he said, adding that he appreciates Paxton's lawsuits against the federal government.

Several dozen Paxton supporters lined up early to sit in the gallery, many of them wearing red.

When Ken and Angela Paxton each walked onto the Senate floor Tuesday morning -- at separate times -- a few people in the gallery called out to them, and the couple waved back and smiled.

They chatted briefly on the floor before the proceedings began and gave each other a kiss.

This story and headline have been updated with additional information.