Explosive allegations from an upcoming memoir by former National Security Advisor John Bolton are strengthening the case for additional witnesses at the Senate impeachment trial of President Donald Trump.

According to Bolton's manuscript, the President sought as recently as September to withhold $391 million in congressionally approved aid to Ukraine until its President announced investigations into his political rival, former Vice President Joe Biden.

Bolton's testimony under oath could answer the key question at the heart of Trump's impeachment, while providing the firsthand account of events Republicans claim to want to hear.

With such bombshell allegations dropped by Bolton, it's tough for Republican Senators—who took an oath of impartiality at the beginning of the trial—to make the case against hearing him testify under oath.

Even Conservative Fox and Friendsco-hosts Ainsely Earhardt and Brian Kilmeade made the surprising admission that they, too, think Bolton needs to testify before the Senate.

Watch below.

Kilmeade said:

"When Lindsey Graham comes out and says Bolton may be a relevant witness, I don't see how you avoid bringing Bolton in now."

Co-host Steve Doocy expressed skepticism before Earhardt concurred with Kilmeade:

"Well, I understand why now many of them want to question him. I didn't want witnesses. I wanted this thing to be over, but now, if he is saying there was a tie — the money in exchange for an investigation — if he is saying that, then some of these senators that have grappled with whether or not to call witnesses, this might be the tip of the iceberg for them."

Earhardt later clarified that she meant "a tipping point," and not "the tip of the iceberg."

A top Republican talking point against the impeachment effort is a lack of firsthand witnesses (though they rarely acknowledge this is due to stonewalling from the White House). Now that a firsthand witness has presented himself, Republican lawmakers are looking for excuses not to hear him.

Some, like Congresswoman Debbie Lesko (R-AZ), say the House should have subpoenaed Bolton instead of getting the Senate to do the House's job (it's the Senate's job as well to hear witnesses). Others like Senator Ted Cruz (R-TX) say the revelations don't change anything.

The Fox and Friends hosts dissent marked a possible epoch.

The President just happened to go on a Twitter screed against Fox News this morning.

It's unclear if Kilmeade and Earhardt will be back tomorrow morning with a new spin, but for now, having Bolton testify—especially with the assurance that the Senate is highly unlikely to convict Trump—may be the prudent move for Republican Senators, even if it's damaging to Trump.