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.
Read More 140 things you don't know about Twitter
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: