LexisNexis Academic now makes it easy to focus a search within government and political blogs, including Twitter. This collection includes blogs by commentators as well as many elected officials.
You can locate this group file in the source directory in LexisNexis Academic by doing a Find on the word blogs. Or you can use this direct link:
http://www.lexisnexis.com/us/lnacademic/api/version1/sf?shr=t&sfi=AC00NBGenSrch&csi=300273
Once you have selected this source, you can filter for a specific blog using the PUBLICATION segment, for example: PUBLICATION(cantor) returns posts from Rep. Eric Cantor’s Twitter blog.