In fewer than 6 hours after that tweet, Obama had amassed more than a million followers.
Prior to Monday, actor Robert Downey Jr. had reached 1 million followers faster than anyone else after an initial tweet. He managed that feat in about 23 hours last year.
This is not Obama's first tweet: The president used to tweet from @BarackObama, but that was taken over by grassroots group Organizing for Action when he took office. Since assuming the presidency, he has occasionally tweeted from that account and @WhiteHouse—signing his tweets "-BO."
Here are some of the responses from political colleagues, CNBC staff and others to Obama's new social media profile: