(CNN) Donald Trump l-o-v-e-s a good plot twist. And that's what he gave political Washington on Tuesday when news broke that Trump had asked embattled chief of staff John Kelly to stay on through the 2020 election -- and that Kelly had agreed.

The narrative of the last few months in Washington had been Kelly's isolation from Trump and the increasing likelihood that the chief of staff would leave 1600 Pennsylvania sooner rather than later. Wrote Politico's Eliana Johnson just two days ago

"A year into the job, Kelly's attempts to implement traditional processes in an untraditional White House have failed, according to a dozen people in and outside the administration. ... Kelly, people around him say, no longer works to keep his mercurial boss on task or on message, with a Republican close to the White House referring to him as a "chief of staff in name only."

How the heck did we go from "Kelly is a dead man walking" to "Kelly is in through 2020?" Lots of reasons -- from the fact that Trump likes to upset expectations and keep his staff on their toes to the fact that replacing Kelly at the moment might have been more trouble than it's worth given the chaos surrounding the President's handling of the ongoing special counsel probe into attempted Russian interference in the 2016 election.

I'd be wary, however, of falling into the "why" trap on this Kelly announcement. Because analyzing "why" Trump reversed course on Kelly suggests that this pact to keep Kelly on through the 2020 election will actually hold all the way through 2020.

And if Trump is Trump and history is any guide, it won't.

That doesn't mean that Trump and Kelly don't believe as of today that their partnership will last as long as advertised. They do! Think of it like junior high school when you and your friend pledge that you will be best friends forever. In that moment, you both totally believe it. But life intrudes. You go to different high schools. Or you go to the same high school but grow apart. Or you go to different colleges. Life happens.

That's sort of how you should think of this Trump-Kelly announcement. Trump is hugely mercurial. There is a reason that everyone assumed Kelly would be gone sometime soon -- because aides, channeling Trump, told reporters that the President was sick of Kelly and wanted him gone. Trump appears to have changed his mind on the Kelly question sometime recently (and, as I note above, for reasons that can be guessed at but never truly known). Trump may totally mean to keep Kelly on through 2020 as of today. In a month, he may have totally changed his mind.

All you need to know about Trump's mindset when he made this offer to Kelly is that the President initially asked him to stay in the job through the end of his second term in 2024, according to CNN's Kaitlan Collins . 2024! That would make Kelly the longest-serving chief of staff ever, far surpassing Andy Card, who stayed in the top job for President George W. Bush for five years.

Given what we know about Trump's lack of long-term strategic planning, it's very, very hard to imagine that Trump thought totally through the idea of Kelly staying on for the next six years -- or even the next two-plus years. Trump decided -- likely in the spur of the moment -- to keep Kelly and, because the President doesn't do anything halfway, offered Kelly to stay on for as long as Trump could possibly hope to be President.

Trump knows a few important things about making a move like that.

First, there's zero penalty for changing your mind. Everyone in the White House serves at the pleasure of the President -- more so with this President than most. If in six months Trump gets rid of Kelly, does anyone think that he would pay a price for it -- with voters or with Republican members of Congress? Answer: No.

Second, Trump has made clear time and time again that he believes he is the only person who matters in the White House (or the broader government). "Let me tell you, the one that matters is me," Trump said in November 2017. "I'm the only one that matters, because when it comes to it, that's what the policy is going to be. You've seen that, you've seen it strongly." He was talking about openings in the State Department, but the idea applies. Trump views himself as the only indispensable piece in the White House. He is, in his own mind, the best chief of staff, communications director and, well, everything else that exists in Washington (or the world).

So Kelly's role -- at least what the role has become -- is to, largely, let Trump be Trump and stay out of the way. Which is not the typical job description of a chief of staff.

In short: Donald Trump and John Kelly have a partnership. For now.