(AP) - House Democrats opened arguments in President Donald Trump's impeachment trial Wednesday, appealing to skeptical Republican senators to join them in voting to remove Trump from office to “protect our democracy.”

Trump's lawyers sat by, waiting their turn, while he blasted the proceedings from afar, threatening jokingly to face off with the Democrats by coming to “sit right in the front row and stare at their corrupt faces.”

Democratic accusers say Trump was the one with the “corrupt scheme” to abuse his presidential power and then obstruct Congress' investigation.

The challenge before the House managers is clear. Democrats have 24 hours over the next three days to prosecute the charges against Trump, trying to win over not just fidgety senators sitting silently in the chamber but an American public, deeply divided over the president and his impeachment.

Rep. Adam Schiff, the Democratic chairman of the House Intelligence Committee, appealed to senators not to be “cynical” about the politics of impeachment, asking them to draw on the intent of the nation's Founding Fathers who provided the remedy of impeachment.

“Over the coming days, we will present to you-and to the American people-the extensive evidence collected during the House’s impeachment inquiry into the president’s abuse of power,” said Schiff, standing before the senators. “You will hear their testimony at the same time as the American people. That is, if you will allow it.”

The proceedings are unfolding at the start of an election year and there are few signs that Republican are interested in calling more witnesses or going beyond a fast-track assessment to bring a quick vote on charges related to Trump’s dealings with Ukraine.

The trial marks just the third time the Senate has weighed whether an American president should be removed from office. Democrats argue Trump abused his office by asking Ukraine to investigate political rivals while withholding crucial military aid, and also obstructed Congress by refusing to turn over documents or allow officials to testify in the House probe. Republicans have defended Trump’s actions and cast the process as a politically motivated effort to weaken the president in the midst of his reelection campaign.

A new poll from The Associated Press-NORC Center for Public Affairs Research shows the public is slightly more likely to say the Senate should convict and remove Trump from office than to say it should not, 45% to 40%. But a sizable percentage, 14%, say they don’t know enough to have an opinion.

One question there’s wide agreement on: Trump should allow top aides to appear as witnesses at the trial. About 7 in 10 said so, including majorities of Republicans and Democrats, according to the poll.

The idea over witnesses, though, seems all but settled after wrangling over rules for the trial stretched late into the previous night, with Republicans shooting down one-by-one Democratic efforts to get Trump aides including former national security adviser John Bolton, Secretary of State Mike Pompeo, and acting chief of staff Mick Mulvaney, to testify as witnesses.

Senators are likely to repeat those rejections next week, shutting out any chance of new testimony.

Chief Justice John Roberts gaveled openWednesday's session as senators settled in for the long days ahead.

Trump, who was in Davos, Switzerland, attending a global economic forum, praised his legal team, and suggested he would be open to his advisers testifying, though that seems unlikely. He said here were “national security” concerns that would stand in the way.

After the House prosecutors present their case, the president's lawyers will follow with another 24 hours over three days to mount a defense. They are expected to take only Sunday off.

Then there will be 16 hours for senators, who must sit quietly at their desks, no speeches or cellphones, to ask written question, and another four hours for deliberations.

By the end of next week there is expected to be one last vote on whether or not they want to hear from more witnesses, and it appears increasingly likely that will be the end.

The impeachment trial is set against the backdrop of the 2020 election. All four senators who are Democratic presidential candidates were off the campaign trail, seated as jurors.

Ahead of opening arguments, Republicans appeared to mock assertions by Democrats that they had overwhelming evidence against the president.

"I am really excited to see this overwhelming evidence," said Sen. Joni Ernst of Iowa. "And once we’ve heard that overwhelming evidence," she added, raising her voice sarcastically, “I don’t know that we’ll need to see additional witnesses, but let’s hear about that overwhelming evidence.”

The trial began with a setback for Republican Senate leader Mitch McConnell, who backed off his plans to limit each side’s arguments to two days, as the White House had preferred.

But the GOP leader has been skilled at keeping even the most wayward Republicans, those with some concerns about Trump, united in batting back Democratic requests for witnesses and testimony. They ultimately approved a rules package that pushes off a final decision on whether or not to seek additional testimony until later in the trial.

Senate Democratic Leader Chuck Schumer bemoaned the limitations, saying Wednesday the impeachment trial “begins with a cloud hanging over it, a cloud of unfairness.”

Republicans were eager for a swift trial. Yet Trump’s legal team passed on an opportunity to file a motion to dismiss the case on Wednesday, an acknowledgement that there were not enough Republican votes to support it.

Procedural wrangling and political posturing dominated the trial’s opening this week, but those steps quickly began to take on tone and content of opening arguments.

The White House legal team, in its court filings and presentations, has not disputed Trump's actions. But the lawyers insist the president did nothing wrong.

“Absolutely no case,” said White House Counsel Pat Cipollone.