@engineer,
Before Johnson only one serving minister had found to lie to parliament, Profumo, and he resigned.
There is to be an inquiry as to whether or not he mislead parliament.
There is a lot of discussion of this on the Brexit thread.
Johnson may have his own base similar to Trump, but they're mostly disgruntled ex Ukipers and far righters, not the majority of Tory grassroots at all.
Johnson was highly charismatic, with an affable bumbling persona which meant he could get away with things other politicians couldn't.
He had cultivated an image for himself on comedy shows Like Have I Got News For You long before he went into politics proper.
All this meant he was able to get away with things for so long that he just didn't bother.
It was the lies, and acting like he and his cronies were above the law.
The first sign was the revolt over him trying to change the rules for his friend Owen Patterson. And it's been downhill ever since.