It could be that this is massive, and has little or nothing to do with the US presidential election. They're going to try to force their way into social by grafting social media posts onto the one thing basically everyone uses - the search page.
Not-a-disclaimer: I'm spending the year at Google (as a visiting scientist; I don't own stock and have no financial interest in its success). You might be surprised by how strong the desire is to do the right thing by users and make it easy for them to find what they're looking for. There's not always an ulterior motive -- happy searchers made Google what it is today.
1600 Mystic John Ray, later repurposed by Karl Marx.
This is just a new ad unit.
Wasn't that the strategy with Google Plus when it came out?