In a past election on another SE site, negative comments on a nomination probably (IMO) contributed to a candidate not being elected.
- The comments were not attacks on the person and not cranky in any way.
- They were presented in a very matter-of-fact way: "I think this candidate's statements A and B mean that they are likely to do C and D and I think C and D are not desirable."
- They were made by a long-standing, active member of the site
- Some other active members agreed with the sentiments expressed
By contrast, in a more recent election, comments on a nomination might have had a Streisand effect, contributing to a candidate's election:
- In this case, there were many serious comments, mostly not made in a very matter-of-fact manner - more like "You're kidding, right?! You can't possibly think this guy would make a good mod!?!"
- Many of the comments were made by people who are not active members on the site.
- Many of the comments were made by SE staff including ones who used to be active on the site but hadn't been seen much for a few years. So these came across as the powers-that-be jumping in on something they didn't understand.
- Multiple people who are active on the site strongly disagreed with the comments.
(But on review, to find all the relevant comments, you also have to browse some of the Qs on meta.ServerFault. I'm too lazy to post links, but there are 4 questions in a row on Nov 20 and 21 2014 that I was thinking of when I made this post. )
If it were me, if I had what I thought was a serious concern that I could express in a dispassionate way, I'd certainly post it on the person's nomination. I would guess that if it's a concern that not many others share, it wouldn't have much impact. OTOH, maybe there are other people who would agree with you, they're just waiting for someone to be brave and take the first step...