During his presidential campaign, Barack Obama made extensive use of social media to rally his supporters. In the process, he produced one of the best case studies yet on how to achieve results with social media.

Post-election, Obama’s use of social media has changed a bit but he’s still making use of it.

In his push for healthcare reform, Obama is encouraging Americans to make their tweets heard through a feature on BarackObama.com called Tweet Your Senator. It’s a simple concept: enter your zip code and a tweet will be prepared voicing your support for healthcare reform to the Senator in your area.

The tweets are well-crafted: if the Senator is on Twitter, it’ll @ them, they include hashtags (one of which, #hc09, is a trending topic) and a link back to the feature on BarackObama.com so that others can tweet their Senators too.

But is this an effective grassroots mobilization tool or little more than a novelty? By all appearances, it looks like the latter.

First, it’s questionable as to how many of the tweets will actually reach the Senators they’re directed to. Not all of the Senators are on Twitter and it’s unclear how many of the ones who are tweeting actually use Twitter to track messages from constituents.

Second, it’s hard to believe that automated tweets such as “Every American family deserves quality health insurance now. Please pass the bill” and “Please support meaningful health insurance reform now” are going to make an impact. While a cynic might argue that politicians don’t listen to their constituents anyway, I’d argue most politicians are far more likely to listen to personalized messages that explain a constituent’s beliefs. Telling your Senator to support healthcare reform in 140 characters on Twitter is probably a lot less convincing than sending a letter explaining personally why healthcare reform would be so important to you.

Which leads to the point of this post: I think there’s a valuable but subtle lesson about social media here.

Obama’s push for healthcare reform hasn’t been so smooth and reports indicate that public support for his plan is now under 50%. In the absence of strong support for his plan, Obama’s grassroots efforts, which not only include Twitter but also include supporter-organized events, are having far less of an impact than the same types of grassroots efforts had during his campaign.

From my perspective, this demonstrates the most important factor in social media success: your message. More to the point, success is derived from the message, not the medium.

During the campaign, Obama’s message resonated strongly and his adoption of social media created a powerful platform for those who wanted to carry his message far and wide. During his push for healthcare reform, the numbers indicate that the message isn’t resonating as strongly. And so it’s no surprise that Obama’s use of social media today looks a lot less remarkable.

This is a good reminder for individuals and brands looking to spread a message with social media but who are focusing far more on the medium.