I disagree.
I think it started with Cameron being gullibled into allowing the Brexit referendum. We were going downhill by then anyway but that vote killed our relationship with Europe and we've been on a downward spiral ever since. Who'd have thought it could have got worse than Johnson?!
I doubly disagree (in part anyway).
For all their failures and shortcomings, it really went downhill for them with the handling of and Boris's partying through the covid pandemic.
As for Cameron, he was obviously electable. I am still astounded and partly mystified as to how he won a majority in 2015 on a ticket of more austerity.
One thing Jeremy Corbyn did do well was highlight the unfairness of austerity on poorer people and public services. The debate on austerity really started to change under his watch as Labour leader.
Other factors constantly undermining the tory's electability were and are numerous incompetent ministers who lack basic common sense. We also now have a war in Ukraine, and the consequential cost of living crisis, so you have the perfect storm.
Technically DO is right in that when Cameron allowed the E.U referendum the party's popularity gradually decreased thereafter, apart from one spike in popularity in the 2019 election when Boris beat Corbyn.
But coming to back Cameron, much as I think he got his austerity economics the wrong way around, in that surely the rich should pay more taxes to balance the books as opposed to the poor and public services, Cameron, like him or deteste him, was a relative electorial success for the tories.
He got turkeys to vote for christmas after the economic crisis of 2008 and that took some doing!!!
Gordon Brown said at the start David Cameron was a salesman and that's exactly what he was. Good for the tories but bad for the wider country and poorer people and public services.