This post has been updated with the latest news that Chaffetz has announced his retirement Thursday from Congress.

A month ago, Rep. Jason Chaffetz (R-Utah) was so over this Congress thing. One of the House's highest-profile Republicans abruptly announced in an April Facebook post he was retiring soon.

A day ago, Chaffetz was so back-into this Congress thing. On Wednesday, he announced the oversight committee he chairs is requesting documents from the FBI related to whether President Trump may have tried to intercede in an FBI investigation into his then-national security adviser, Michael Flynn.

It was a significantly aggressive step from a committee chair who, up until this point, had backed away from investigating the Trump administration. And it was a complete 180 for a congressman who had one foot out the door.

On Thursday, another 180: Chaffetz has announced he's leaving Congress in June to work in the private sector. He'll be leaving the probe he started 24 hours ago in limbo. It's not clear who would lead the committee he'll be vacating, nor whether that person will continue to look into whether Trump tried to block the FBI's Russia probe.

Speaker Paul Ryan (R-Wis.) said on May 18 that he has not spoken with Rep. Jason Chaffetz (R-Utah) about his timeline for leaving office. (Reuters)

He's out, he's in, he's out again. What's going on? The best we can surmise, it comes down to one word: Ambition. And Chaffetz's rapidly changing calculations about what best fits him.

When Chaffetz first announced his retirement, we surmised that he was ditching Congress because he decided it just wasn't fun anymore. As chairman of the House Oversight and Government Reform Committee, Chaffetz is in charge of investigating wrongdoing in the government. And it's way more fun to investigate your political opponents' wrongdoing than the candidate you supported (kinda) for president.

So pleased she is not the President. I thanked her for her service and wished her luck. The investigation continues.

A post shared by Jason Chaffetz (@jasoninthehouse) on

But the wave of damning news crashing into team Trump this week suggests there could be wrongdoing in the government that was too big for Chaffetz to resist. He sent a fiery letter the FBI requesting all documentation related to the now-fired FBI director James B. Comey:

“According to [the New York Times], 'Mr. Comey created similar memos — including some that are classified — about every phone call and meeting he had with the president.' If true, these memoranda raise questions as to whether the President attempted to influence or impede the FBI's investigation as it relates to Lt. Gen Flynn. So the Committee can consider that question, and others, provide, no later than May 24, 2017, all memoranda, notes, summaries, and recording referring or relating to any communications between Comey and the President.”

If the FBI doesn't hand this over willingly, Chaffetz indicated he'd be ready to force it with a subpoena.

And Chaffetz made a big deal on Twitter Wednesday about Comey coming to testify to his committee:

"I think it's worthy of investigation," he told Fox News's Tucker Carlson on Wednesday.

Gauntlet thrown. Now the rest of House Republicans have to decide if they'll side with Chaffetz that Congress should pursue what Trump allegedly told Comey, wherever the facts may lead.

Chaffetz was in the center of the action — where people who know him say he thrives. Maybe Congress even started to be fun again without Hillary Clinton's emails to investigate.

But that doesn't explain why Chaffetz is announcing his departure a day after inserting himself into one of the biggest political news stories of Washington. Chaffetz's staff told The Fix on Wednesday his mindset is: He'll keep doing his job while he's in the job.

"My life has undergone some big changes over the last 18 months," he wrote in a letter to his constituents Thursday. "Those changes have been good. But as I celebrated my 50th birthday in March, the reality of spending more than 1,500 nights away from my family over eight years hit me harder than it had before."

We also know that Chaffetz is a guy whose career appears to be almost singularly driven by ambition. He briefly ran for speaker of the House in 2015. He's more likely than not to run for governor of Utah in 2020. His sometimes head-spinning positions make a little more sense when seen through the lens of getting elected to that next big job.

Take, for instance, another flip-flop in recent Chaffetz history: In October, he ditched Trump after the “Access Hollywood” tapes, saying he couldn't defend that kind of person to his 15-year-old daughter. But a few weeks later, he said he'd vote for Trump:

In October, Chaffetz may well have been disgusted by what Trump said on a hot mic. But he soon calculated that at least voting for Trump, the Republican nominee for president, was a requisite to advancing in the Republican Party.

A month ago, Chaffetz calculated that staying in Congress was a political dud for his political future. A day ago, Chaffetz calculated that being in Congress isn't so bad after all for a politically ambitious lawmaker. Twenty-four hours later, he calculated that it wasn't. Only time will tell why.

Rep. Jason Chaffetz (R-Utah) got a frosty reception in his home state on Feb. 9, at a town hall. Angry constituents packed a high school auditorium, grilled the high-ranking congressman with questions and peppered him with boos and chants while protesters amassed outside. (Jenny Starrs/The Washington Post)