That being said, another axiom of politics already verified to a certainty is that low approval numbers going into elections are increasingly difficult to reverse relative to chronological proximity to election day. IOW, the closer election day gets, the harder low approval numbers are to reverse. 

All of this depends of course on accurate polling numbers - which the 2016 election of DJT revealed as largely bogus - so internal polling (as performed by the respective parties) would be the indicator most would follow (or only polls where respondents may remain anonymous).