At approximately 2:30 p.m., Pierce posted, "Y'all as tempting as it may be, don't shoot Obama. We need him to go down in history as the WORST president we've EVER had! #2012."
The tweet came hours after police arrested a man for firing shots at the White House, leaving two bullets in the executive mansion.
Pierce told ABC News that the comment was a "joke" and that the "whole [shooting incident] was stupid." Giggling, she said that an attempted assassination would "only make the situation worse."
"Insofar as she's a representative [of the College Republicans], maybe it shouldn't be said, but she's made a positive statement in a way," said Cassie Wright, the group's vice president.
"I don't really see anything wrong with it," Wright added. "It's just a personal comment, not representative of any group. Just freedom of speech, you know?"
Amid growing attention, Pierce removed the post and apologized on Twitter for her actions.
"It's never funny to joke about such a serious matter," she said. "I have learned a very valuable lesson."