When John Bolton left his position as President Trump's national security adviser, the president tweeted out his version of Bolton's departure, and Bolton responded with his own, contrasting version.  After that he remained relatively quiet until Monday, when he emerged to remind everyone that he's out there and willing to talk.

John Bolton served as Donald Trump's NSA from April 2018 to September 2019.  It was not a happy working relationship.  The men clashed over the aggressive positions Bolton staked out regarding Venezuela, North Korea, and Afghanistan, positions that did not fit well with Trump's more isolationist instincts and desire for mutually agreeable solutions.

It should therefore not have come as a surprise to anyone when, on September 10, 2019, Trump abruptly tweeted that he was letting Bolton go:

I informed John Bolton last night that his services are no longer needed at the White House. I disagreed strongly with many of his suggestions, as did others in the Administration, and therefore....

— Donald J. Trump (@realDonaldTrump) September 10, 2019

....I asked John for his resignation, which was given to me this morning. I thank John very much for his service. I will be naming a new National Security Advisor next week.

— Donald J. Trump (@realDonaldTrump) September 10, 2019

It should be noted that Trump did not insult Bolton's qualifications, skills, commitment, or personality.  He simply stated that their policy differences meant that they could not work together.  Bolton, however, who is known for his combativeness, contested Trump's characterization of events:

I offered to resign last night and President Trump said, "Let's talk about it tomorrow."

— John Bolton (@AmbJohnBolton) September 10, 2019

Bolton doubled down on his statement when he started a P.R. war against Trump by texting various reporters to tell them what boils down to "He didn't fire me; I quit."  Bolton then went silent on his personal Twitter account for two months, only to return and blame the White House for using software to shut down that account.

White House spokesperson Stephanie Grisham politely suggested that maybe Bolton was having age-related technology issues.  Overall, it was not an edifying spectacle.

Apparently still smarting from his disputes with Trump, Bolton has put himself back in the news, this time by issuing a statement on January 6 that, after wrestling for some minutes with his conscience, he has decided that he will testify in the Senate against Trump...not that anyone has formally asked him to do so. 

During the present impeachment controversy, I have tried to meet my obligations both as a citizen and as former National Security Advisor. My colleague, Dr. Charles Kupperman, faced with a House committee subpoena on the one hand, and a Presidential directive not to testify on the other, sought final resolution of this Constitutional conflict from the Federal judiciary. After my counsel informed the House committee that I too would seek judicial resolution of these Constitutional issues, the committee chose not to subpoena me. Nevertheless, I publicly resolved to be guided by the outcome of Dr. Kupperman's case.

But both the President and the House of Representatives opposed his effort on jurisdictional grounds, and each other on the merits. The House committee went so far as to withdraw its subpoena to Dr. Kupperman in a deliberate attempt to moot the case and deprive the court of jurisdiction. Judge Richard Leon, in a carefully reasoned opinion on December 30, held Dr. Kupperman's case to be moot, and therefore did not reach the separation-of-powers issues.

The House has concluded its Constitutional responsibility by adopting Articles of Impeachment related to the Ukraine matter. It now falls to the Senate to fulfill its Constitutional obligation to try impeachments, and it does not appear possible that a final judicial resolution of the still-unanswered Constitutional questions can be obtained before the Senate acts.

Accordingly, since my testimony is once again at issue, I have had to resolve the serious competing issues as best I could, based on careful consideration and study. I have concluded that, if the Senate issues a subpoena for my testimony, I am prepared to testify.

Translated, what Bolton has said is that he was originally waiting to see what the federal court would say about whether his colleague, Dr. Charles Kupperman, should respond to congressional subpoenas.  Because the issue became moot before the court issued a ruling, Bolton decided to forgo a judicial ruling and unilaterally offer himself as a witness.

It is unlikely that, if the matter ever gets to the Senate, President Trump will call Bolton to testify.  Nevertheless, Democrats and NeverTrumps got excited.  Sen. Mitt Romney, whom Trump treated with surprising graciousness and who then responded with vicious spite, naturally announced instantly that he wanted to hear from Bolton.  And of course, Sen. Chuck Schumer enthusiastically endorsed the idea of having Romney testify.

As long as Cocaine Mitch is in control, though, Bolton's supply will not be met with demand.