(CNN) At 1 p.m. ET on Wednesday, impeachment manager Rep. Adam Schiff opened the House's presentation to remove President Donald Trump from office.
By 2 p.m., Republican Sen. Bill Cassidy of Louisiana had yawned, pushed away from his desk and ate a piece of chocolate. By 3:30 p.m., there were 17 empty seats, as senators stood along the walls of the chamber or hung back in the party's private cloakrooms.
By the time Rep. Jerry Nadler, a New York Democrat and another House impeachment manager, began talking around 4 p.m. ET, that number had grown to about two dozen, as senators rolled back into the chamber from a break.
While the Senate won't determine a verdict for over a week, it's clear that a number of senators are not only tired, but have already made up their minds, raising further the expectation that it will vote to acquit.
Over the past few months, administration officials have testified that Trump pressured Ukrainian President Volodymyr Zelensky to announce an investigation to damage 2020 candidate and former Vice President Joe Biden and his son, Hunter Biden, who once sat on the board of a Ukrainian energy company. Some of the witnesses for the House impeachment inquiry -- including career and political State Department officials -- have alleged that Trump used a coveted White House visit and hundreds of millions of dollars in US aid as leverage. There is no evidence of wrongdoing by either Biden in Ukraine.
The Constitution requires two-thirds of the Senate to remove Trump from office. The House alleges two crimes -- abuse of power and obstruction of Congress -- but on its first day delivering its argument, the prosecution appears unlikely to convict. Republicans in the Senate majority have indicated in the past couple of days that they will vote to acquit.
On Tuesday, GOP Sen. Tom Cotton of Arkansas openly dismissed the House managers, who tried to no avail to convince enough Republicans to join Democrats in allowing new witnesses. When Rep. Hakeem Jeffries of New York said Trump had committed crimes, Cotton scoffed. When Rep. Jason Crow of Colorado said only the Senate could fix this national crisis, Cotton rolled his eyes. When Schiff said late at night that his California district might be watching, Cotton laughed.
Sen. Josh Hawley of Missouri told reporters that Trump had done nothing wrong and was ready to vote. Hawley said the prosecution and defense would just present the trial briefs in his brown, fan folder. "We all can read," he said.
The prosecution did not appear to make much progress with Republicans on Wednesday.
Before the House managers even began to make their case, Cassidy tweeted in the morning that it was "very weak." Sen. Lindsey Graham of South Carolina held a news conference to say it would be an "uphill battle" for him to vote to convict, since "the best group of people to pick a president are the voters -- not a bunch of partisan politicians."
In the afternoon, Sen. John Cornyn of Texas said he was "struggling to see how" Trump's actions were "even close" to meeting the Constitution's standard of removing the President from office. On Fox News, Sen. David Perdue of Georgia called the articles of impeachment "illegitimate," and "the fruit from a poisonous tree." Sen. Mike Braun of Indiana said he "never" condoned Trump's actions, but added that they were "clearly" not impeachable offenses.
A few minutes after Schiff began talking, Kentucky Sen. Rand Paul of Kentucky said on Twitter, "The more we hear from Adam Schiff, the more the GOP is getting unified against this partisan charade!" He then invited Trump to attend the trial. Later, Paul studied a crossword puzzle as the prosecution deliberated on the Senate floor.
Some Democrats have also already said that they would vote to convict. When asked if she hoped her party would vote together to do so, Sen. Mazie Hirono of Hawaii said on Wednesday, "I hope so."
But even if all 47 Democrats stuck together, they need 20 Republicans to break from their party leader to remove him from office. The managers' immediate goal is a more manageable task: convincing just four Republicans to allow them to subpoena crucial witnesses who have not testified, including former national security adviser John Bolton.
About half of Americans say the Senate should vote to convict Trump and remove him from office, while nearly 70% of Americans say that the trial should feature testimony from new witnesses, according to a recent CNN poll. The Senate will vote on whether to subpoena witnesses after each side presents their case.
Still, Trump's allies are confident that they will prevail.
"I have no doubt, based on the facts that I've been able to see and read and hear, and based on the facts that they're about to see and hear and read, that they will acquit based on those facts," said Republican Rep. Mark Meadows of North Carolina.
This story has been updated with additional developments Thursday.