Scum-watch: Backing Boris.
Not to get too deep into this, or to indulge too much in Sun Kremlinology, but as we know because he's told us, the Sun wouldn't have come to the decision to back Boris without Murdoch himself giving the OK. On the surface, it's a no-brainer: Livingstone and the right-wing press have in the past, and right up to the present day in the Evening Standard's case, had a relationship akin to that of Tina and Ike Turner. They hated him, and he hates them even more, even though he's taken money off both the Standard and the Sun in the past by writing for them. Boris might be a buffoon, but he's an buffoon that'll sell newspapers, is the Troll's view.
The decision is interesting from my perspective because as previously noted, Murdoch doesn't necessarily support the candidate that has the most in common with his own views, he supports those who are going to win, and who are least likely to affect his business interests. The two are also inter-linked: Murdoch gives support, leader/party ensures that nothing untoward happens to his interests, hence why Blair so viciously shot down anyone who dared to squeak against the Sun or otherwise. Johnson, however, is certainly not the dead cert that Blair was in 97 when the Sun, after being the most Thatcherite of Thatcherite papers, became the most Blairite of Blairite papers. Indeed, today's latest poll shows that Ken has gone back into the lead.
Murdoch's reasoning seems to be thus: if Johnson wins, and does well, then it will be a perfect springboard for the paper to then put its weight behind Cameron's Conservatives, who up until recently both he and the Sun have mostly either ignored or put down. If Johnson wins and does badly, then it'll help inform whether he duly does decide that the Conservatives are worth supporting once again. If Ken wins and Murdoch and the Sun end up with egg on their face, then it doesn't matter on the scale that it would if the Sun backed the wrong side in a general election. As always, whatever happens, Murdoch wins, and we lose.