... looking into my rather grubby crystal ball here are some possibilities ....
- Trump's behaviour becomes even more erratic precipitating a major world crisis &/or a series of bungled decisions affecting international relations, the UK in particular. May's handholding is seen as desperately poor judgment & compromising Britain's reputation. As we all know, once the Tories sniff weakness in their leader they'll go in for the kill. There could also be some score settling after the post-Referendum fall-out. (Watch Gove).
- Voter fatigue &/or general disenchantment with May & her cabinet coupled with some as yet unanticipated scandal(s). Boris can still be relied upon to deliver a major embarrassment & this will erode support. The Media frenzy itself could lead to many switching off.
- Ukip antics muddy the water to such an extent that what had seemed reliable Tory votes are lost to Farage's bully boys - expect plenty of misinformation & rumour (e.g. that the Tories cannot be relied on to see Brexit through properly ...)
- A weird pact uniting various No to Brexit groups (Greens, Lib Dems, etc.) which draws a substantial enough following of the disaffected - including some of the unconvinced Tory vote
- A wild card - some major event which transforms popular opinion. Some options: 1) catastrophic mistake in the NHS; 2) another banking collapse; 3) terrorist or other attack/outrage; 4) constitutional crisis (the Queen etc.); 5) environmental disaster ... which in each case are seen to be related to government incompetence or duplicity. Extraordinarily Labour (with or without Corbyn) seems a better option - at least untainted by the mess.
The outcome? Not the resounding win that May expected but a split vote. No one party in control. A disunited kingdom with running sores of Scotland, Ireland & Wales as well as damaged relations with Europe, the USA, & the rest of the world. May - like Cameron before her - revealed as the chancers they are.
The crystal ball clouds ...