What done for Tony Blair was his closeness to George W Bush and one of the things doing for Theresa May is her closeness to the man who overtook Bush as the worst US President in living memory, Donald Trump.
A pathological liar, the links to Russia are the latest in a long line of lies which he or his family dismiss as fake but have turned out to be true.
Within days the 'big nothing-burger', a harmless chat about adoption with a Russian official, went to a confirmed attempt by a foreign nation to undermine Hillary Clinton and American democracy in the 2016 election,
Following the denials, along came Trump junior himself to release an email chain showing that in fact he took the meeting in anticipation of receiving dirt on his fathers rival on the explicit understanding that this was part of a Russian government effort to help the election of his father.
Theresa May tied herself to Trump in the first week of his presidency, rushing to Washington to hold his hand and offer him the bauble of a state visit.
When Trump broke from the Paris agreement on climate change, May refused to sign, saying she would raise the subject with him at the G20 meeting only to admit afterwards that she had done no such thing.
When he was widely condemned for leaving his daughter in his G20 seat while he stepped out of a meeting, May, said that she thought it 'entirely reasonable'.
While derided as less than a joke and a liability to keen at arms length around the World, May continues to hitch her star to a President that was always likely to explode in her face.
Already weakened at home by a range of awful decisions, May manoeuvring herself so closely to such an embarrassment of an American President who quite rightly attracts such vitriol is baffling.