10 Moments That Changed Doctor Who Forever
4. "Don't You Think She Looks Tired?"
At the end of World War Three, the Doctor informs Rose that Harriet Jones will go on to be Prime Minister for three successive terms, becoming the architect of Britain’s Golden Age.
So it must've come as a bit of a shock to the timeline when, only a few months later, the freshly-regenerated Tenth Doctor has her premiership cut short with six simple words:
“Don't you think she looks tired?”
Beyond the (potentially huge) implications of the Doctor casually changing the entire course of British history, this moment had much more immediate ramifications for the UK.
By kneecapping Harriet's political career so soon, the Doctor inadvertently kicked off a chain of events that would end in Harold Saxon being elected Prime Minister.
And we all know how that went.
Without the power vacuum and ensuing political upheaval caused by Harriet's golden age falling apart, the Master wouldn’t have been able to infiltrate British politics, which, among other things, resulted in the death of the US President on live TV – one of the few events that wasn't undone when time was rolled back in the Series 3 finale.