Personally, I'm very disappointed with the level of support for open source I've seen. A Github account with a dozen or so projects all related to a CMS is not what I call supporting open source. At best its a concession to the developers you've attracted to help with your political platform. You just won't get certain developers if you don't also allow them to participate in open source. It's calculated and expedient here more than altruistic or in the name or transparency, openness and letting the American people own the works for hire they have paid for through taxes.
If he (or any politician) wants to really support the idea of open-source they would require that everything that can be open-sourced will be open-sourced. The only exception I see to open-sourcing would be limited to almost strictly to military or defense related software and hardware projects. For every single other system, the source code should be out there in the public. Start with every single non-critical piece of software that is not part of infrastructure like transportation and public utilities and once security practices and norms improve and stabilize among the non-critical stuff, slowly and carefully open source all the rest except for military and defense projects.
At the price tax payers are paying for software, we should own the code outright many many times over.