Adrien Friggeri has a lovely visualization of US Senators movement between clusters:
You have to click the image and play with it to appreciate it. The methodology isn’t yet published – but I can see how this could be very illuminating. The dynamic clustering aspect hasn’t been researched much – one of the notable pieces is the Blei and Lafferty dynamic topic model of Science.
I did a static analysis of the US Senate back in 2005 with Wray Buntine and coauthors. Some additional visualizations and the source code are here. We did a dynamic analysis of US Supreme Court on this blog but there’s also a paper.
My knowledge on this topic is out of date, however. Who has been doing good work in this area? I’ll organize the links.