Merriam-Webster's online dictionary defines privacy as "freedom from unauthorized intrusion." The United States government defines privacy as "freedom from unauthorized intrusion, except by us." Personally I prefer the former definition.
The site allows for those "cosponsoring" and "tracking" bills to receive updates that are not defined. Will these updates be managed by the Majority Leader's office? If so, are they partisan messages from the Republican Caucus or will they be couched as updates from the institution of "Congress"?
Google clearly defines how your personal data is being collected and used. Google uses this data for a number of reasons which are spelled out in the privacy statement. And only Google uses your information, unless you have given them opt-in consent.