Otherwise known as Trump and Brexit! Given that both outcomes were completely unexpected the left in the US and the UK immediately went to work to reverse both! Pelosi and Bercow understand that reversing these outcomes without a clear mandate to do so could create an even bigger problem for them.
In the UK that would be the election of their version of Trump, Boris Johnson which would then be followed by a Brexit without an exit agreement with the EU. In the USA that would be a failed impeachment effort to remove Trump followed by his re-election in 2020.