With opposition parties in disarray, May has seized on a strong moment to win her own negotiating mandate from the British people. She can deal a hammer blow to the Labour Party, which is split by internal divisions over Brexit. And she can potentially silence dissent within her own party about any compromises she makes with EU leaders as they divvy up their divorce settlement.
Perhaps most importantly, she can put off the next round of elections until 2022, offering more breathing room for both sides as they rush to complete Brexit negotiations before Britain leaves the European Union in 2019.
If she hadn't called new elections, she would have had to face voters in 2020 at the latest, increasing election-year pressures in a settlement that is sure to be painful for both sides.
But if she thinks a stronger domestic mandate will blow down doors in Brussels and force them to make concessions, she is likely mistaken. Above all, the election will add yet more uncertainty in an topsy-turvy Europe that is already facing the possibility that an anti-EU leader could win the French presidency next month and that German Chancellor Angela Merkel could be unseated in September. "I guess we had too much political stability in Europe," wrote the director of the Carnegie Europe think tank, Tomas Valasek, on Twitter.
And May's own apparent red lines – including strong barriers against a new movement of EU workers to Britain and no role for the European Court of Justice in policing the Brexit deal – increase the likelihood that EU leaders will take a tough stance against her, no matter the view of the British people.
The Greek government made the miscalculation of using elections as a negotiating tactic in 2015 when it held a referendum about whether to accept the terms of a painful bailout deal. Greek voters rejected the deal – but EU leaders didn't budge.
So far, EU leaders have taken a hard and unified line on Brexit, saying that they will offer few concessions on access to Europe's borderless market without rights for their own citizens and businesses inside Britain. They owe nothing to British voters.
Despite the grim chances for the snap polls to reverse Brexit momentum, opponents of the divorce are seizing this as their last, best chance to turn the tide. Britain's Liberal Democrats, which ruled alongside May's Conservatives until 2015, said that people who believed Britain should remain closely tied to the European Union now had a chance.
"If you want to avoid a disastrous Hard Brexit. If you want to keep Britain in the Single Market. If you want a Britain that is open, tolerant and united, this is your chance," Liberal Democrat leader Tim Farron said in a statement.
But in a measure of the unlikeliness that the basic Brexit dynamic will shift, the Liberal Democrats are only polling at about 10 percent in most recent surveys, compared to more than 40 percent for the Conservatives.
And Labour Party leader Jeremy Corbyn did not even mention Brexit in his initial response to the snap election call, a sign that he does not intend to focus on the central question of British political life in his bid to gain seats. Now, instead, the bigger question will most likely be whether an increased majority for the Conservatives emboldens the hard-line backbenchers who want a tough Brexit, or whether May can quiet them and seek a more conciliatory line.