The reality of the situation is the time for that is November 6th and later (or during the primaries or the last 4 years).

For the months between the primary concluding and the general election concluding, if you support the candidate, then criticism is a distraction that undermines the goal of getting them elected.

So you are free to criticize of course, but it’s a practical concern to be aware of that you are convincing others to not vote at all or vote against the candidate.