The Grenada invasion was already started when the bomb went off, Reagan had his hands full, his eye was on the big picture that was seen as impossible to accomplish at the time, (destroying the Soviet Empire) and he made the right decision to not become mired in the Middle East.
Being less than Reagan I wanted revenge, but he was right and was fighting a global war for mankind and the future, a lessor man would have reacted emotionally.
Reagan made a mistake in Lebanon and knew it.