Now they have discovered that she is a much more artful politician than many had realised, who may well have had this in mind for some time.
She is also a gambler, which is an even greater revelation than discovering that she is an opportunist.
By and large, prime ministers do not like early elections. To go to the country is to risk everything, whatever the polls say. That is why so many have clung to office with small majorities or even with a minority sustained by cobbled-together coalitions.
So Theresa May's Downing Street demarche setting an election date for June 8 was an astonishing act of political courage, or should it all go wrong, of hubris.
Conventional wisdom holds that she will win a landslide; and in normal times, with such a poll lead, she would.
But these are not normal times. However much the parties try to address domestic issues, this will be the Brexit election and risks being a re-run of the EU referendum campaign. Suddenly, millions of Remainers who thought the chances of stopping or ameliorating Brexit had gone for good have been given another chance.
How many will take it is the biggest unknown for May, though given Labour's position perhaps it is less of a risk than it might have otherwise have been. After all, will even the most ardent Remainer really risk having Jeremy Corbyn as PM, even in a coalition?
Corbyn said he "welcomed" the opportunity to challenge the Government on its economic and social policies. But he is heading for a disaster at least on a par with Labour's showing under Michael Foot in 1983. Then, Margaret Thatcher won a majority of 144 and May is evidently hoping for something similar. She not only needs to win; she needs to win big.
The stakes could not be higher. May, whose personal ratings are better than almost any prime minister at this stage of a premiership, can secure her own mandate, exterminate the Labour Party, marginalise Ukip and reinforce her position ahead of negotiations with the EU.
She has confounded those who regarded her as overly cautious and indecisive, evincing a steeliness and self-belief that may well convince the country she is exactly the person needed to take Britain through turbulent times. Then again, if she has miscalculated the consequences will be calamitous for her and her party.