(CNN) President Donald Trump's former national security adviser John Bolton announced in an unexpected and newsworthy statement Monday that he is prepared to testify if issued a subpoena as part of a Senate impeachment trial.
This is important for a number of reasons. Here are four:
Remember, Bolton's lawyer indicated during the House inquiry phase -- way back in November! -- that it would be worth investigators' while to get him on the record, writing that he had been directly privy to "many relevant meetings and conversations that have not yet been discussed in the testimonies thus far." But Bolton did not testify during the House impeachment hearings.
While he's been silent, honoring a request by Trump not to talk, he featured prominently in much of the impeachment testimony. We know that he thought of the effort to pressure the Ukrainians for investigations beneficial to Trump as a sort of "drug deal," according to Fiona Hill, the White House's former top Russia expert.
Now he is on the four-person Senate trial witness wish list issued by Minority Leader Chuck Schumer on behalf of Senate Democrats. (The other three are acting White House chief of staff Mick Mulvaney, Office of Management and Budget official Michael Duffey and White House aide Robert Blair, who is Mulvaney's national security adviser.)
Under the leadership of Majority Leader Mitch McConnell, Republicans have largely opposed the idea of witnesses at a Senate impeachment trial. Even those like Maine's Sen. Susan Collins and Alaska's Sen. Lisa Murkowski, who have expressed some frustration with the process, have not definitively said they would support voting with Democrats for new testimony at an impeachment trial.
So Bolton is volunteering to do something there's a very good chance he'll never have to do. But in his statement he refers to his "obligations as both a citizen and as former National Security Adviser," as if they are in conflict.
Bolton is a Republican, but of the neoconservative hawk variety, and he clashed with Trump during his time at the White House, particularly with regard to North Korea and Syria. He was unceremoniously dumped by tweet in September.
He's been happy and quite complimentary on Twitter of Trump's combative new approach to Iran. But the idea that a former staffer is teasing that he's got a story to tell can't be what the White House or Trump wants to hear.
Bolton was never technically issued a subpoena by House impeachment investigators because he said he would testify only if compelled by the courts. House Democrats, confident they had the goods on Trump, didn't want to spend the time waiting for the courts. Bolton asked them to keep up the court fight, but a judge dismissed the relevant case, which actually concerned a former Bolton deputy, after the House impeached Trump.
Now Bolton says he won't need to wait for the courts. After careful consideration, and since the courts won't be weighing in before a Senate trial, he's "prepared to testify."
Bolton certainly has a tale to tell, as he's repeatedly made clear. It's important to note that he's writing a book that's meant to be published before the 2020 election. This publicity is in his interest. If he had a smoking gun, so to speak, he could just say it.
Hill, who reported to Bolton at the National Security Council, testified about his disapproval of Trump's efforts to pressure Ukraine to investigate former Vice President Joe Biden and his son Hunter's relationship with Burisma, a Ukrainian natural gas company.
"I am not part of this, whatever drug deal that Mulvaney and Sondland are cooking up," she said Bolton instructed her to inform a lawyer on the National Security Council about his position with regard to Ukraine. Watch that testimony.
We also know from the testimony of Hill's successor, Tim Morrison, that Bolton had a meeting with Trump specifically about Ukraine. And again: Bolton's own attorney said in encouraging House Democrats to seek his testimony in the courts that he had knowledge of meetings not discussed during the impeachment inquiry.
Democrats are saying -- They've argued that Bolton's statement shows Nancy Pelosi's strategy of withholding the articles of impeachment from the Senate in hopes of getting a more fair trial is working. Remember, it takes four Republicans voting with Democrats to compel testimony.
Schumer promised Monday to force votes on witness testimony. "A trial without all the facts is a farce," he said, seeding the idea that acquittal will be meaningless without witness testimony. "The verdicts of kangaroo court are empty."
Republicans are saying -- Sen. Shelley Moore Capito, a West Virginia Republican, would not say if she would vote to subpoena Bolton or if she wants to hear testimony from him. "I'm just going to wait and see what happens," she said.
This is in line with McConnell's preference that senators hear arguments about impeachment first and then decided whether to call witnesses.
Sen. Susan Collins of Maine, who is facing a tough reelection campaign, said she's open to witnesses later on, after arguments and after senators have a chance to ask questions.
"There are a number of witnesses that may well be appropriate," she said.
Another endangered Republican, Sen. Martha McSally of Arizona, just said senators are working through all of this.
The opposition force -- Sen. Marco Rubio of Florida, a member of the Senate Intelligence Committee, told CNN he would not vote for a subpoena of Bolton because it was the House of Representatives' job to get his testimony.
"If the House wants to start a new impeachment inquiry or pull it back and add additional elements to it, that's their choice to make," he said.
Ahem, Sen. Rubio. Two previous presidential impeachments featured fresh witness testimony in the Senate trial.
Protecting the Senate from a 'circus' -- Sen. John Cornyn of Texas, a member of the Republican leadership team, evolved over the course of the day, according to CNN's Phil Mattingly and Ted Barrett.
Cornyn initially told reporters he "has no objection" to Bolton testifying "by deposition or some prerecorded testimony."
But he later indicated he would not vote to subpoena Bolton and warned against a "circus-like atmosphere" like the one he believes there was in the House.
Cornyn also repeatedly said he thought Bolton's testimony would be stifled by executive privilege, which he said would likely be invoked by Trump on much of what Bolton would have to say.
The topic of Bolton and how the issue of witnesses affects a Senate trial took over the Impeachment Watch Podcast on Monday. David Chalian and I talked to Alice Stewart, the GOP strategist and CNN analyst, about whether she'd advise purple-state Republicans to vote with Democrats on the issue.
"It's so sad for our country," Trump told the conservative radio host during a phone-in interview. "We're fighting with Iran, we're fighting with all of these different places -- and in many cases doing great, making trade deals and doing so good -- but I have to spend, and my team has to spend, time on this stuff."
Asked what he thought was behind Speaker Nancy Pelosi's decision to withhold sending the articles of impeachment to the Senate, Trump responded: "Well, I think what they're trying to do is affect the election, illegally, but that's what they're trying to do. The reason they're not sending them is because they're -- they are a joke. They are not crimes. There's nothing there."
Sometimes nothing is as refreshing to read as "we don't know."
CNN's Phil Mattingly has an incredibly informative piece about how McConnell, Pelosi and Schumer all continue to circle each other as Pelosi refuses to send the articles of impeachment to a Senate where the leader has said he's coordinating with the White House unless she can be assured of a fair trial.
To questions like "When will the trial begin?" Mattingly is not afraid to say we don't know. Because we don't.
One thing he says we do know is that McConnell will not attempt to change Senate rules to proceed with a trial before Pelosi officially transmits the articles of impeachment.
Why? It would effectively end the legislative filibuster and McConnell has shown no interest in doing that.
The President has invited foreign powers to interfere in the US presidential election. Democrats impeached him for it. A Senate trial is next. It is a crossroads for the American system of government as the President tries to change what's acceptable for US politicians. This newsletter will focus on this consequential moment in US history.
Keep track of the action with CNN's Impeachment Tracker. See a timeline of events. And get your full refresher on who's who in this drama.