Hillary Clinton’s health scare could easily turn into a nightmare for her campaign.

That’s because it not only raises questions about her health, but gets to the heart of her problem with voters, the majority of whom say she is not honest and trustworthy. In an appearance this morning on Fox and Friends, Donald Trump signaled that this is the approach he’s going to take in addressing the issue, questioning when Clinton had been diagnosed with pneumonia (her campaign revealed the diagnosis last night):

The relevant part of the transcript:

I hope she gets well soon. I don’t know what’s going on. I’m like you—I see what I see. The coughing fit was a week ago, so I assume that was pneumonia also. I mean, I would think it would have been, so something is going on, but I just hope she gets well and gets back on the trail, and we’ll be seeing her at the debate.

Between the well-wishes, you can see the seeds of doubt that Trump is hoping to sow. “I see what I see” = The video of her stumbling after the 9/11 ceremony was alarming. “The coughing fit was a week ago” = She clearly had an ongoing health issue, which her campaign didn’t divulge. “Something is going on” = Hillary is hiding something!

The best way for Clinton to counteract all of this is to be as transparent as possible. But that is not the way Clinton operates, and Huma Abedin is already telling staffers, “Onward as H.R.C. would say.” This is a mistake.