“Not only have I never heard the ‘head on the pike’ line but also I know of no Republican senator who has been threatened in any way by anyone in the administration,” Collins said.

Schiff’s comment in the Senate chamber was clearly a key moment in the trial, and it came at the end of another long day in which the California Democrat otherwise effectively prosecuted the case that Trump abused his power in requesting investigations into his political opponents and withheld aid to Ukraine.

But as the night came to a close, Schiff, the House Intelligence chairman, was talking about the complicated politics of the impeachment trial and how different his own safe district might be from battleground states where GOP senators will soon face voters. Then as he wrapped up his case and read the quote from a CBS story: That a Trump ally said "GOP senators were warned ... 'vote against the president and your head will be on a pike.'"

The mood in the room shifted entirely. Several Republican senator murmured "not true" as soon as Schiff said it. Collins shook her head and said "not true" several times. Schiff quickly tried to recover.

"I don't know if that's true. But when I read that, I was struck by the irony," Schiff said. "I hope it's not true. I hope it's not true."

There is simply no arguing that Trump demands loyalty of his party and has resorted to veiled threats against Republicans who don’t give him what he wants. As former Sen. Dean Heller (R-Nev.) criticized efforts to repeal Obamacare, Trump mused about whether Heller "wants to remain a senator" while sitting beside him. He trashed House Republicans that lost in 2018 after distancing themselves to him. And during critical moments, he publicly urges the party to stick together on his Twitter feed.

But after a long day of arguments, Schiff's closing comments became the only moment Republicans will remember. And the GOP outrage swelled, some manufactured and some legitimate.

"No Republican senator has been told that," said Sen. John Barrasso (R-Wyo.), who has mocked the impeachment trial. "What he has proven to all of us is he is capable of falsehoods and will tell it to the country. And would tell it to us when we are sitting in the Senate chamber. When every one of us knows it is not true."

Democrats suggested many in the GOP were simply waiting for a moment to latch onto, just as they did earlier in the week when House Judiciary Chairman Jerry Nadler (D-N.Y.) said the Republicans were abetting a "cover-up" and were taking votes that are "treacherous."

Sen. Chris Murphy (D-Conn.) acknowledged it was "the first time the GOP audibly grumbles during the entire trial. But c'mon — like it's totally implausible that one of Trump's sycophants would say that?" And Sen. Chris Coons (D-Del.) said it was clear Republicans "reacted sort of viscerally and immediately to that particular line" but scoffed at the idea that would be a reason to vote against witnesses.

"If that's your reason? That he mis-cited some press article? Come on," said Coons. Schiff "turned to a conversation about political retribution that struck a discordant note. But our job is to sit here and weigh the evidence. And a misstep for three sentences in a closing, doesn't affect the evidence at all."

On Saturday, Schiff defended himself from the GOP hand-wringing: "If the worst they can point to is I referred to a published report in CBS? That's pretty thin gruel."

Most Republicans were never going to be swayed by Schiff, so his misstep is unlikely to determine Trump's fate. But annoying the likes of Murkowski, Collins and retiring Sen. Lamar Alexander (R-Tenn.) just days before the Senate will vote on whether or not to consider witnesses clearly didn't help win any votes either.

"It was a really dumb moment on his part," said Sen. Kevin Cramer (R-N.D.), who was another senator who verbally raised objections to Schiff in the chamber. "Susan, her and Lamar are like the conscience of the institution, they really are ... one thing about Adam Schiff is if he would stop an hour earlier every day he'd be better off. Last night too is when he landed flat. He just sort of blew it. But tonight was really dumb."

"I don't know why he would do that. That could have been left out, that's for sure," said Sen. Joe Manchin (D-W.Va.), who wants witnesses and could in theory be swayed to acquit the president. Manchin said Schiff was "very articulate" and "very compelling" but Manchin acknowledged the misstep: "A lot of my colleagues, it was upsetting to them."

Marianne LeVine and James Arkin contributed to this report.