The race is now down to 5. (From 21!)
What's changed in their website setups?
Donald Trump got rid of Flash, otherwise everything else appears to be the same.
Ted Cruz went from a A+ rating to just an A (lost HSTS?).
Nothing changed for John Kasich.
Hillary Clinton went from an inconsistent server setup with many IPv4 addresses to just 1 IPV4 address. The www. redirect behavior (from without to it) does mess up HTTPS Everywhere and ssllabs tests. A major plus is she added HSTS to her site, so her ssllabs rating is now A+.
Bernie Sanders added IPv6 support and HSTS to the main site. Unfortunately a sha2 intermediate certificate prevents his site from going from A to A+. And his donation provider has HSTS setup correctly and get's an A+.
At this point in the campaign, only A ratings (ssllabs) are left! The Democrats seem to have prioritized implementing HSTS, but neither appears to have gone for the preload list.
HSTS - Means you tell the browser to enforce SSL
I also included sub domains in this list, but it wasn't as interesting as I hoped.