People have written more than 12,000 tweets using the phrase "assassinate Trump" since inauguration, Mashable reports. Now, the Secret Service is working to distinguish the jokes from those with serious intentions. One man was already charged for tweeting "My life goal is to assassinate Trump" the night of the election. The Secret Service is investigating a woman who tweeted "If someone was cruel enough to assassinate MLK, maybe someone will be kind enough to assassinate Trump." But none of the Trump assassination tweeters contacted by Mashable have gotten in trouble so far. Facebook and Twitter ordinarily remove posts containing death threats, but they don't seem to have kept up with the influx of Trump assassination posts. Tim Franklin, a criminology and criminal justice professor who used to be a Secret Service agent, believes Trump's been getting more backlash over social media than past presidents because he himself uses Twitter so much. It could also be related to the fact that he has the lowest approval rating of any recent president. But the Secret Service will only come after people who seem like they have "a true and genuine intent to do harm," Franklin told the site. "They're not going to to beat down the door of everybody who makes a negative Twitter comment."