For some reason, the install bootstrapper for 3.5.3 x86 embedded the wrong hash value for launcher.msi. As a result, it will fail to download the file and install will be aborted.

The workaround is to deselect the launcher from being installed, and use the 64-bit installer to install the launcher. Or alternatively, install Python 3.6 to get the later version of the installer, which will then automatically skip it for the 3.5 installer.

Python 3.6 is unaffected, so this may just have been a build glitch, but it needs investigation and testing so it doesn't happen again. (Adding a /layout test after uploading is an easy way to test this.)