But then, everything came tumbling down: her authority and government were severely weakened as she lost her Parliamentary majority.
Now, the British media's adjectives of choice for May are "beleaguered," "weak," "isolated."
And yet, in a party not short of ambitious members, she remains Prime Minister. The fragility of her leadership and her government seems to be suspending everything delicately in place.
Given her weakness then, you'd think Theresa May would be an easy target for MPs to fire political ammo at her without fear of retribution.
Exhibit A: Boris Johnson. The star of the former Foreign Secretary's has waned as some MPs have been turned off by his public criticism of the Prime Minister in lengthy pieces in British press, his outspoken condemnation of the Prime Minister's Brexit policy -- not to mention his regular appearances in reports of leadership plots.
This time last year a former co-Party Chairman, Grant Schapps, led a failed coup to topple the Prime Minister, which was exposed by 10 Downing Street.
The backlash was strong and swift. Schapps said: "The level of abuse and bile which has rained down since is simply unprecedented in my own experience of politics, and I've been a party chairman at election time, so that's saying something!"
For a Prime Minister that had cut the party's majority a few months earlier and was the target of widespread anger as a result, the knee-jerk counterattack against the plotters was surprising.
Most recently, Conservative MP James Duddrige announced that he had submitted a letter of no confidence (48 are needed before a no-confidence vote is called) in May shortly before her keynote conference speech.
Duddrige claimed he hadn't met one MP who thought May would lead the party into the next election. An ally of Johnson, he said, "Boris is a rock star. He is a vote-winner, he is a leader -- and she is neither of these."
May's unexpectedly disarming conference speech followed, exhorting the party to come together, or Brexit is at risk. Duddrige's move fell flat and had no real impact whatsoever.
Members murmur about when to depose May and whom to replace her with, but anyone who crosses the line to coup ends up far worse off.
Since Michael Gove famously turned on his one-time pick for PM, Boris Johnson, in the 2016 leadership contest, backstabbing has gone out of fashion. Besides, he who wields the knife will never wear the crown.
At the Conservative Party Conference in Birmingham this week, it was clear that Johnson's teasing of May (he appeared on the front pages of many newspapers on Tuesday morning running through a field, a mocking reference to the time the PM said that it was the naughtiest thing she had ever done) and the response of European leaders to her at the informal summit in Salzburg has encouraged some Cabinet members and activists to rally around her.
Maybe May gives human form to Brexiteers' angst at how they believe the European Union has treated the UK. Maybe her public and constant knocks are relatable. Either way, she has engendered a begrudging respect and sympathy. But don't mistake this for popularity.
Since the bungled snap election of 2017, May does not enjoy great support within her party and her authority is indiscernible (cautious and infrequent reshuffles are one symptom of this).
There is a leadership vacuum. So much so it seems like the post of prime minister has never been so up for grabs. But instead of the available support coalescing around a candidate, the party is splintered: on Brexit, on the domestic agenda and what they want the personality of their future leader to be.
There are too many ill-defined and rival visions for the future as to render her opposition formless. Nevertheless, factional agitating in the Conservative Party continues, depleting May's opponents of political energy and capital.
Not to mention the difficulty May is having selling her Brexit plan and the thorny negotiation process of dealing with the EU. The issue is so divisive that it is hard to see an outcome of which Parliament or the public would approve. Brexit is a political poisoned chalice which even politicians aspiring to be prime minister may hesitate to drink from.
Testament to May's perceived weakness as a leader is the notion that the Conservative Party could not be sure of an election victory if one was called tomorrow.
Polling supports this. She polls closely, if slightly above the unreservedly socialist leader of the opposition, Jeremy Corbyn.
It's exactly this weakness that gives May an incongruous strength. For many hard Brexiteers, who predominantly populate the right wing of the Conservative Party, there might be one fear greater than no Brexit at all: Jeremy Corbyn inside Downing Street.
The fear of triggering an election -- one that the Conservative Party could easily lose -- is keeping some of the voices in the party in check. For now, at least.
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