The headline here is possibly a bit misleading.

Its not clear that Paul Ryan had previously taken a position on SOPA. However, Paul Ryan faces a credible challenge in the upcoming election from Rob Zerban, and that makes him vulnerable. Zerban had taken a clear anti-SOPA position. Therefore, a great deal of support flooded in to him from grassroots opponents of SOPA organizing via Reddit. Ryan has therefore announced that he does not support SOPA.

A sustained campaign coordinated by redditors has evidently convinced Congressman Paul Ryan (R-WI), the House Budget Chair, to drop his support for the Stop Online Piracy Act.

More here:

On the heels of this news, Paul Ryan has announced he will not support SOPA legislation. After receiving large contributions from pro-SOPA interests, Paul Ryan was put on the defensive. Rob Zerban lent his full and early support to the independent effort to stop this legislation, and joined the movement to stop this online on sites including Facebook, Twitter, and the online community of Reddit. Zerban's efforts received the attention of many online, especially the Reddit community, resulting in significant unexpected contributions and thousands of new volunteers and supporters.

Paul Ryan's decision, as a partisan leader and head of the Budget Committee, to back away from legislation actively pursued by another Republican Committee Chair, is a major accomplishment. Americans organized online and achieved significant policy impact in very little time. It showed even a high and mighty leader, considered by many as extreme, realizes he is accountable to the public through their online efforts.

Lamar "I Can't Hear You!" Smith does not seem to have a serious challenger in the upcoming election.

Congressman drops support for SOPA - Boing Boing