As much as I loathe the Bible belt Christians and jihadists, we might remember that much the same was tried here, at the Admiral Duncan in Soho ... just happened that the bomber wasn't as thorough as the speciman(s) in Orlando.
....it did help that he didn't have easy access to guns, though. The Admiral Duncan explosion and a couple of others that month in London were crude, home-made bombs made with powder from fireworks.