WASHINGTON — Twitter has fast become the conventional-wisdom clearinghouse and real-time echo chamber for major political events, so it was not surprising Tuesday evening when Twitter also became the forum where opinion on President Obama’s State of the Union address seemed to crystallize before he had even finished speaking.

“The media party line where everyone can listen in,” said Mike Murphy, a Republican strategist.

“The town hall for the media and political elite,” said Erik Smith, a Democratic strategist and founder of Blue Engine Message and Media.

The power of Twitter to shape the debate (for better or worse) was on display shortly before Mr. Obama began, when Representative Randy Weber, Republican of Texas, posted an error-riddled message that called the president a “Socialistic dictator,” and quickly went viral.

Indeed, Twitter’s ability to focus the pundit class helps explain why, in the fierce competition to control the political narrative, lawmakers, candidates, operatives and even the president are increasingly turning to it and other social media. The battle is the same as before, but they are now hoping to prevail 140 characters at a time.