They haven't got someone near half way sane, none of them are. It's a misconception that this is all down to Truss, they were sliding well before she was put in charge
Even the immigration topic appears to be slipping away from them
Just to be clear how bad they are, the last time they were this low in the opinion polls was 1994-95 in the build up to the 1997 General election. It took them 15 years to get re-elected.
In 1995 they got a bounce when John Major was re-elected leader, it wasn't big enough tosave them, not by a long way. They already tried the new leader bounce trick twice and failed miserably
This is what a death spiral looks like