It's not even 24 hours since the PM called the general election she said she wouldn't call.
It's the opposite of Gordon Brown's "election that never was", rather the "election that wasn't meant to be".
Much will be written about her motivations for the U-turn, the change of heart that led her to this point. The long-term view of her motivation will in time be coloured by the eventual result of course.
But as the unofficial day one of this campaign draws to a close, some things are clear.
For months there has been a pretty straightforward balance sheet of advantages and disadvantages to holding an early poll. Theresa May believed it tipped to holding firm.
There were plenty of reasons for going early - most temptingly making the most of Labour's weakness to grab dozens of seats.
It would free Theresa May from the strictures of the 2015 manifesto - she's already proved she doesn't feel much constrained by that - which no one who remains in government had involvement in putting together.
It would give her her own mandate, even though PMs are not directly elected. It would draw a line between her leadership and David Cameron's, once and for all.
And with a likely majority, IF the polls are correct, it would make it easier for her to get her Brexit plans through Parliament, give her more freedom to pursue her other - some controversial - plans like reintroducing grammars, and strengthen her hand with EU leaders as she gets down to negotiations.
Going early could also minimise the potential fallout over the Tory expenses saga - a bad hangover from the 2015 election.
In the negative column:
- The embarrassment of a U-turn
- The political inconvenience of getting round the Fixed Term Parliament Act
- The self-inflicted instability at a time when the PM has preached the opposite
- The missed opportunity of holding an election before the boundary changes that give the Tories an extra, notional 20 seats or so
- Having an election during the Article 50 process
- Probably above all else, the simple unpredictability of holding an election when no politician in 2017 can be completely sure what the outcome will be
Until only a few days ago it was those arguments that held sway.
Theresa May has shown time and again that she is willing to change her mind when the facts change.
For example, she and her chancellor dropped a major plank of his Budget in only a week when they saw resistance, and the government junked a review of the powers of the House of Lords.
Her public argument for calling an election - that it was resistance from the opposition and the Lords over Brexit - does not quite tell the full story.
Parliament has been tricky for the PM, but certainly not impossible.
Notwithstanding that, nor the factors that have created strong political arguments for taking the plunge in the last couple of months, senior government sources point to a specific factor that changed the prime minister's calculation.
The end of the likely tortuous Article 50 negotiations is a hard deadline set for March 2019.
Under the Fixed Term Parliaments Act, that's when the Tories would be starting to prepare for a general election the following year, with what one cabinet minister described as certain "political needs".
In other words, the government would be exposed to hardball from the EU because ministers would be desperate to avoid accepting anything that would be politically unpopular, or hold the Brexit process up, at the start of a crucial election cycle.
As one insider put it: "We'd be vulnerable to the rest of the EU in 2019 because they know we'd have to move fast."
Ministers say that's the central reason for Mrs May's change of heart because "if there was an election in three years, we'd be up against the clock".
By holding the election now, Theresa May hopes she gains a fresh start on the political clock on Brexit, even though the Article 50 process still has a deadline of only two years.
This gives what was described as "flexibility over the logistics of Brexit… we don't have to pretend we can do it all in two years".
'Window' of opportunity
That's not to say for a second this means departure from the EU will be held up. The Article 50 process will proceed, the government says, exactly as planned.
But, if the Tories win, an early election may have bought ministers some valuable breathing space to work out what the UK really looks like outside the EU.
They'll have, in theory, three years after exit for things to settle down before the public get another chance to have their say.
That timetabling question was not her only reason, as outlined above.
But after the EU's initial brush off after the Article 50 letter, that argument became more compelling.
The PM's conclusion was that the best way of her going into those negotiations in as strong a position as possible, was by taking advantage of the window between the French and German elections before the EU gets down to proper business.
A hypothetically bigger majority of course also acts to neutralise the cruelly dubbed "Remoaners" in her own party, and the far larger, and much more powerful, group of ardent Leavers who have been able to exert a lot of pressure.
But while the polls suggest an early election could make many of her political problems disappear, polls prove nothing.
Politics in 2017, as we've discussed again and again, is unpredictable and taking bets is a fool's game. The reasons Theresa May hung back from an early election haven't disappeared.
PS: Westminster's guessing game has been who knew, and when.
No one will confirm officially on the record. For what it's worth, sources tell me that David Davis and Philip Hammond were the only ministers who were extensively consulted.
Both Boris Johnson and Amber Rudd were told before Tuesday morning's cabinet meeting. But there were ministers around the cabinet table who had no idea and who were, it's said, visibly shocked when Mrs May told them.
The cabinet was kept in the cabinet room during the announcement, and watched it on TV.
The mood was apparently very enthusiastic, with one moment of huge laughter when the wifi link that was playing her announcement on the screen in the street just outside broke down and the PM suddenly went to black.
Apparently the glitch was sorted within a few seconds, but her colleagues will hope the PM is better at running an election campaign than sorting out the Number 10 broadband.