She has, the argument goes, not been endorsed by the voters at the ballot box, or by her own party members in a full leadership election - Mrs May was simply the last one standing after Andrea Leadsom pulled out of the race.
Opponents claim she lacks a mandate, while some on her own side urged her to call an early election. After all, the Tories enjoy a double-digit lead in the polls, and there is no prospect of replacing Jeremy Corbyn with a more popular leader.
Talk of an early vote intensified after the High Court ruled that MPs should be given a vote on Article 50 before the formal exit process from the EU is triggered. Most MPs campaigned to remain in the EU, and the working Tory Commons majority is just 14 after two back-bench resignations in the past month. If the government doesn’t win its appeal to the Supreme Court, some have warned that parliament could derail Mrs May’s Brexit timetable.
The Prime Minister has stood firm, saying she won’t call an early vote, but has left herself a little room for manoeuvre, saying the next election “should” be in 2020.
So why won’t she?
There are a few clues in today’s leaked memo on the government’s Brexit preparations.
The focus is on the headline assessment that the civil service is swamped by preparation work for negotiations, and ministers cannot agree on a Brexit strategy.
But the memo - which, it should be stressed, wasn’t commissioned by government - also makes clear why an early election is at least unlikely.
Firstly, the memo points out new boundary changes that will give the Conservatives a huge boost are due to be introduced in 2019. They still need to be approved by MPs, many of whom are unhappy at the changes, but on current forecasts Labour could lose as many as 30 seats and the Tories could walk away with a majority of up to 100.
Secondly, with government lawyers fighting hard in court to prevent MPs from holding a vote on Article 50, the memo’s authors note that in the current climate, a general election would become a second Brexit referendum by proxy, airing all the detail about upcoming negotiations with Brussels that ministers want to keep under wraps - something I suggested a couple of weeks ago.
There are a few other good reasons not to go to the country, too. Parties prepare for months to face off in a national campaign, but while the opposition are gearing up for battle, the Tories don’t seem to be in such a hurry.
Reports suggest that only a quarter of the constituencies not currently held by the Conservatives have selected candidates.
It all adds up to the conclusion that when the Prime Minister says no election until 2020, we should take her at face value - for now, at least.