The key thing is the appearance of fairness. While there are some Republicans who might be open to investigating it more, perhaps not enough for an impeachment but enough for a more full investigation, Pelosi's actions made Republican Senators feel that the impeachment was being done more for political points. and so that evidence was hid. As such, it's a lot harder to have good evidence on the issue. Any evidence is not going to be trustworthy if it's gathered in secrecy and in deceptive ways.
A major evidentiary disagreement is over the motives of the president. If he was in good faith pursuing corruption, many don't see that as impeachable. The lack of clarity and bipartisan fairness on the issue helped make them agree.
Republicans say McConnell's job to unite them was also helped by what they say were Democratic missteps: Pelosi's decision to withhold the articles for weeks in an effort to extract concessions from a Republican-controlled Senate and GOP perceptions that Democrats are using impeachment to target vulnerable Republicans.
His strategy of copying the Clinton impeachment articles also helped unify members.
For months, aides and members say McConnell has laid the groundwork for an impeachment process that would somehow shield his vulnerable members from charges of partiality while ultimately leading to Trump's acquittal. McConnell quickly latched onto the idea of using "the Clinton model," a reference to the very first resolution in the Clinton impeachment trial that passed the Senate 100 to 0 and set up a process that allowed both the House managers and the President's defense team to make their cases before lawmakers voted on hearing from witnesses.
This approach convinced key senators that he was being fair while the Republicans were being unfair.
"It's pretty obvious it is not about the President," Sen. John Barrasso, a Republican from Wyoming, told CNN. "It is about Schumer's approach to become the majority leader of the Senate."
"What McConnell did was explain it was a process that had precedent, that was done previously. I saw Trent Lott recently, who was the Republican leader at the time, and he explained it exactly the way McConnell explained it to us," one Republican senator told CNN about how McConnell slowly convinced the conference to adopt his view of how a trial should run.
This lack of fairness has been a continual thing they discussed as important in their decision making.
U.S. Senator John Barrasso (R-WY), chairman of the Senate Republican Conference, issued the following statement after the House of Representatives transmitted articles of impeachment to the Senate.
“Today House Democrats sent to the Senate the most rushed and unfair impeachment articles in modern history. They held secret hearings, released misleading information, and denied the president due process. This was a political stunt. Just one in three Americans say the process in the House was fair. Justice will finally be done – that will be in the Senate.”
So, not rushing impeachment articles, avoiding releasing misleading information, giving the president due process is presumably what they wanted. Adding more evidence wouldn't have necessarily made it better without it being gathered in a fair way.
In terms of persuading McConnel, that's harder. What he wants is a clear lack of partisanship and more effort in making a case.
‘But that’s not what happened this time. House Democrats performed a pale imitation of a real inquiry. They did not pursue their own subpoenas through the courts. They declined to litigate potential questions of privilege. They pulled the plug as soon as Speaker Pelosi realized she had enough Democrat votes to achieve a political outcome.
‘This isn’t really about Ukraine policy or military assistance money. It can’t be. Because, for one thing, prominent Democrats were promising to impeach President Trump years before those events even happened.
So, he would have wanted a longer House trial where they pursued subpoenas through the court and did a more in depth fact finding mission. I have read a lot of his statements. He sees this as a serious issue, the lack of attention to detail. Style over substance. He would also want them to not try to impeach Trump before the supposed impeachment event occurred.
‘And just a few weeks ago, when a reporter asked Speaker Pelosi why the Democrats were in such a hurry, here was her response: “Speed? It’s been going on for 22 months. Two-and-a-half years, actually.”
‘Now, that’s interesting. The events over which Democrats want to impeach happened about six months ago. So how has impeachment been underway for two-and-a-half years?
I haven't seen him comment much on the actual charges- he views them as a political charade, since it was done in a rushed and unfair manner for political gain, and mostly mocks the process. He doesn't believe you should draw conclusions before you have a fair trial because the president and others may have exculpatory evidence they might present if allowed to do so.
There's also a lot of distrust about Schliff not making a parody statement about what the president said, and being deceptive about communication with the whistleblower, [from inside conversations.] which means this distrust of the process is fairly widespread in private as well.
The senators’ opinion of House Intelligence Committee chairman Adam Schiff, one of the impeachment managers, is barely better than that of the president. They simply don’t trust Schiff at all, and feel they have ample reason to not believe anything he says — from his decision to read a parody version of the transcript of Trump’s July 25 phone call with Ukrainian president Volodymyr Zelensky out loud during a hearing, to reports that the whistleblower met with Schiff’s committee before the whistleblower’s complaint was filed, to the chairman’s slippery-at-best description of his interactions with the whistleblower.
There are people more on the fence.
From dozens of interviews with GOP lawmakers, congressional aides and White House staffers over the past month, it’s evident that Rooney is right: There is a sizable number of Republican senators and representatives who believe Trump’s actions are at least theoretically impeachable, who believe a thorough fact-finding mission is necessary, who believe his removal from office is not an altogether radical idea.
But they would need more evidence.
In terms of the evidence that would change the more on the fence people, clear statements of personal interest. More interviews and pursuing of subpoenas of Trump staffers would have helped with this. As noted above though, McConnell's leadership convinced people that finding that evidence was the House's job.
A clear statement of exclusive personal interest would help persuade the more on the fence senators.
Collins: Mr. Chief Justice, I send a question to the desk on behalf of myself, Senator Murkowski, and Senator Romney.
Roberts: This is a question for the counsel for the President. If President Trump had more than one motive for his alleged conduct, such as the pursuit of personal political advantage, rooting out corruption, and the promotion of national interest, how should the Senate consider more than one motive in its assessment of Article I.
Relating to the issue of poor house conduct, the Senate, even those who may believe Trump was wrong, don't want to do the House's job for them. They see it as the House's job to present a case, and don't want to go further than the current evidence.
Republican Sen. Roy Blunt of Missouri, speaking to reporters Friday, was asked if he agreed with Alexander that Trump’s conduct was inappropriate but not impeachable. He responded by saying that he had a “lot of respect for” Alexander and that he opposed hearing from witnesses for what he said were “institutional” reasons.
So, short of some extreme confession from Trump, no additional element is likely to change their mind. That was the House's job.