The race has so far focused on pledges, or non-pledges, to cut taxes, at a time when many parts of the state are struggling to function, along with defence spending, energy policy, Brexit and social issues such as transgender rights.
With both candidates serving in senior jobs in Johnson's government, they may also be limited in their ability to pitch themselves as a fresh start.
Pollster Hopkins said a new party leader "normally gets a small bump in the polls, but it will be an uphill battle to claw support back because this government has been badly damaged".