Typically, responsive web design is leveraged to allow organizations to develop one site that fits all devices, whether it’s viewed on a smartphone, tablet, laptop or desktop. This approach significantly lessens development resources.
A cursory look appears to show that both sites have the same content, so it’s not quite clear what the strategy is.
Perhaps m.state.gov is the beta site for state.gov? Or should be?
Regardless, now that the State Department has a responsive website, my recommendation would be to replace the current state.gov with the m.state.gov and redirect all traffic going to the mobile to the main site.
This lets State significantly reduce its website development and content management costs and allows it to repurpose those resources into building a stronger, unified web presence.