WASHINGTON — The first day of the second impeachment trial of Donald Trump began with a graphic video of the Jan. 6 riot at the U.S. Capitol — and ended with a clue to the endgame.

After a first round of arguments by the House Democratic managers and Trump’s defense team Tuesday, 56 senators voted to dismiss Trump’s constitutional objections and continue with the trial — the latest sign that there won’t be 67 votes to convict.

The trial represents a series of historic firsts: the first trial of a former president, the first time a president has faced two trials and the first time the chief justice of the United States isn’t presiding when a president is on trial.

Here are four takeaways from the first day:

One Republican flips

The Senate has held only two substantive votes so far — not about whether to convict Trump, but about whether it should be holding a trial at all.

Two weeks ago, five Republican senators voted against a motion to dismiss the trial on constitutional grounds: Mitt Romney of Utah, Pat Toomey of Pennsylvania, Lisa Murkowski of Alaska, Susan Collins of Maine and Ben Sasse of Nebraska.

The issue was revisited Tuesday, with each side given two hours to make its case about whether the trial was permitted under the Constitution.

Democratic House impeachment managers were able to change the mind of Sen. Bill Cassidy, R-La. He joined the five other Republicans and all of the Democrats in declaring the trial constitutional.

“The House managers were focused. They were organized. They relied upon both precedent, the Constitution and legal scholars. They made a compelling argument,” Cassidy told reporters after the vote. “President Trump’s team were disorganized. They did everything they could but to talk about the question at hand. And when they talked about it, they kind of glided over it, almost as if they were embarrassed of their arguments.”

The 56-44 vote means the trial will proceed. But it also signals the difficulty Democrats will have in securing a conviction.

Sen. Kevin Cramer, R-N.D., said it is “highly unlikely” that a senator would vote against constitutionality but then vote to convict.

“It’s going to be a hard mental trick to convince yourself that, on the one hand, this is an unconstitutional exercise and, on the other hand, I should be open to conviction,” Cramer said moments before the trial began. “That’s a pretty tough turn for smart people to make.”

Democrats skip right to core of case

The first day was supposed to have been dedicated just to constitutional arguments, and most had imagined that it would be filled with arcane discussions by legal scholars.

But Democrats knew the audience would be large, and they used their most compelling material at the outset: a 13-minute mashup of video clips of the mob storming the Capitol.

The graphic video was spliced with Trump’s speech at the earlier “Stop the Steal” rally. Images of the rioters breaking into the Capitol chanting “fight for Trump!” were mixed with his calls for supporters to head there.

During the video, a Trump supporter yelled at a police officer, “We are listening to Trump — your boss.” The video also included clips of Senate Republican leader Mitch McConnell of Kentucky speaking out against Trump’s effort to overturn the election before both chambers were evacuated as rioters moved in.

“If that’s not an impeachable offense, there is no such thing,” said Rep. Jamie Raskin, D-Md., the lead Democratic manager, arguing that there is no “January exception” to the Constitution.

Trump’s lawyer rambles

Trump attorney Bruce Castor might have stolen the show Tuesday, but it didn’t appear to be by design.

In a presentation that lasted almost an hour, Castor spoke off the cuff, meandering from ancient Greek history to allusions to the Revolutionary War. He discussed a childhood spent listening to former senators like Everett Dirksen.

He talked about Toomey, noting that he is also from Pennsylvania. He sought to flatter Sasse, calling Nebraska a “judicial thinking place.” Both senators are considered swing votes.

Mostly, Castor left senators confused about his point.

“I thought the president’s lawyer, the first lawyer, just rambled on and on and on and didn’t really address the constitutional argument,” Sen. John Cornyn, R-Texas, told reporters.

Trump’s allies tried to spin the confusing presentation as part of a strategy to get away from the emotional Democratic arguments. But later, Castor acknowledged that after they watched the Democrats presentation and video, he and Trump’s other attorney, David Schoen, decided to change course.

“I’ll be quite frank with you. We changed what we were going to do on account that we thought the House managers’ presentation was well done,” Castor said in concluding his remarks.

Managers impress, but to what end?

At the end of the first day, there were no signs that there had been a breakthrough or a revelation that would convict Trump.

“I thought the attorneys were very well prepared and well-spoken. I think, actually, the Democrats sent a better team this year than last,” Sen. Roger Wicker, R-Miss., told reporters.

But he added, “It did not change my mind.”

Julie Tsirkin contributed.