As he made the closing arguments for the House prosecution, Rep. Adam Schiff (D-CA) finished not with an argument to convict the president but a plea for the Republican senators sitting in the chamber to vote for additional evidence, a critical and increasingly imperiled part of the Democratic strategy in the impeachment trial of Donald J. Trump.

He appealed to their sense of duty and fairness—and had the GOP side of the room, if not rapt, at least paying attention.

And then he got ahead of himself.

In the crescendo of his speech, a riff on the difficulty of “moral courage,” Schiff raised a CBS News report from Thursday in which an anonymous Trump confidant said the White House had been warning GOP senators their heads would be on “pikes” if they voted against the president’s desire for a smooth acquittal.

At that moment, Republicans’ disapproval was clear, with several senators piping up to say “that’s not true” or shaking their heads. “I hope it’s not true,” Schiff said repeatedly, before pressing on. “Give America a fair trial. She's worth it,” he concluded.

But afterward, all Republicans could talk about was less the substance of the speech and more Schiff’s raising of the idea that Republicans were under threat from the White House.

“I have not been told that my head is on a pike,” Sen. Lisa Murkowski of Alaska, a key swing vote, told reporters afterward. “I thought he did fine until he overreached.”

Others were more blunt. Sen. James Lankford of Oklahoma complained Schiff was “insulting.”

Even before things got medieval, House Democratic impeachment managers had spent the day hammering home the case that was supposed to sway Republicans and the public on witnesses: that the president had prevented Congress from conducting a full investigation of his conduct.

All the while, however, some Senate Republicans were hard at work crafting reasons why access to additional evidence and witnesses should stay out of sight .

The second article of impeachment passed by the House outlines how President Trump used his power to block access to critical information during their impeachment inquiry—leaving their investigations incomplete and the truth buried.

“No president ever used the official power of his office to prevent witnesses from giving testimony to Congress in such a blanket and indiscriminate manner,” Rep. Zoe Lofgren (D-CA) said from the well of the Senate on Friday. “There is no telling how many government officials would have come forward if the president hadn’t issued this order.”

As a result, Democrats have advocated for the Senate to use its power to subpoena missing documents and individuals to fill in those blanks in order to have a full picture of the president’s actions before they cast a vote to acquit.

But by Friday evening, any senator who would ultimately skip the witness part of the impeachment program appeared to have an answer.

The evidence was overwhelming and complete, it just didn’t prove the case.

There wasn’t enough evidence, the House should have called more witnesses, waited longer for the courts to work through the White House objections.

Even if the witnesses were called, some Republican lawmakers said, the White House would block them anyway, citing executive privilege, and it would take too long to argue with the courts.

Four days into the impeachment trial of President Donald Trump, the tide appeared to be turning against the possibility that new witnesses would appear and fill in the missing details about why the White House made the decision to withhold hundreds of millions of dollars in congressionally approved aid from Ukraine.

At the opening of the trial there had been some cautious, fragile optimism among Senate Democrats that four or more Republicans could join with them to compel the release of new evidence, as Sens. Susan Collins (R-ME) and Mitt Romney (R-UT) signaled they were leaning toward wanting to hear new information. Those Republicans even ensured that the rules included a provision that would have made a vote on individual witnesses, like ex-National Security Adviser John Bolton, a possibility. But just a possibility.

By the end of the week, however, even that chance seemed to be slipping away.

“The House made a decision that they didn't want to slow things down by having to go through the courts,” Sen Lisa Murkowski (R-AK), another potential swing vote, told CNN on Thursday. “And yet now they're basically saying you guys gotta go through the courts. We didn't, but we need you to.”

That vote on whether or not to call for new evidence will come after the president’s defense team presents their case, a process that will begin Saturday and seek to decisively kill any momentum on calling new witnesses. Jay Sekulow, counsel to the president, told reporters on Friday it would serve as something like a “trailer or coming attractions” for their full-length session of argument on Monday.

And any potential Republican support will also have to hold through a lengthy question-and-answer period during which lawmakers will pepper both sides of the impeachment trial with additional questions.

“I, like many others, am still waiting on that overwhelming evidence that must be coming, maybe, later today,” said Sen. Joni Ernst (R-IA), sarcastically. “There must be some earth-shattering news or information that they are going to present to us overwhelming evidence.”

After saying the process was rushed through the House, Sen. Lindsey Graham (R-SC) said calling Bolton, who has indicated he would testify if subpoenaed, would amount to a destruction of executive privilege.

“I am not going to let the House put me in this box of ignoring witnesses and asking me to call them and denied the president his day in court on executive privilege,” said Graham. “And to my Republican friends, you may be upset about what happened in the Ukraine with the Bidens but this is not the venue to litigate that.”

Democrats spent much of Friday pushing back against the Republicans’ “Choose Your Own Adventure” menu of reasons why witnesses should not be called.

Sen. Kirsten Gillibrand (D-NY), for example, rejected the idea that Bolton would be subject to executive privilege and argued other disputes would be resolved quickly due to the presence of Chief Justice John Roberts.

“I think it's a deeply flawed argument, first of all, some of these witnesses aren't under executive privilege, such as Bolton, there is no executive privilege claim for his testimony he's one of the witnesses I want to hear most from,” she said. “Also, I believe, since we have this particular framework, where we have the Chief Justice presiding. The ability to do an expedited legal review is there, it would be very quick, it would be very efficient.”

But the Democrats were left to acknowledge these points were a tough sell. “Frankly,” Sen. Chris Coons (D-DE) told The Daily Beast, “I think there's quite a few in the majority who don't want to be in the awkward position of having to confront the record and the evidence.”

The sense that no dam was breaking—helped along by the GOP’s grab-bag of defenses—caused hope to slowly drain from Democratic lawmakers who had held out hope they might get a critical mass of votes for witnesses.

On Thursday, Sen. Dick Durbin (D-IL), the No. 2 Senate Democrat, said he didn’t assume that there was even a single existing GOP vote for additional witnesses and evidence.

By Friday, Sen. Chris Murphy (D-CT) said “the walls are closing in” on Republicans weighing their witness vote. “I don't understand it,” Murphy said. “But I understand how Mitch McConnell works, and ultimately he feels his job is to protect the president of the United States—not protect the Senate, not protect democracy, not protect this institution.”

Senate Democrats’ frustration on witnesses was compounded because of what they viewed as an effective final day of presentation by the House impeachment managers. Sen. Chris Van Hollen (D-MD) said that the onslaught of arguments is getting through to some of his GOP colleagues—but admitted that political imperatives may win out.

“I know for a fact some Republican senators are very troubled by the evidence they've heard and they are very troubled by the total stonewalling of the administration,” said Van Hollen. “Whether or not they're willing to do something about it, that's a whole other question… They know it's not a ‘perfect’ phone call, and yet they're clearly afraid to say so in public. And that's the root of the problem.”