Divine assassination was evidently a burdensome affair. The thought of injuring or otherwise traumatizing a bystander aroused Guiteau’s greatest apprehensions. He seemed to sincerely believe that he was on a God-given errand. One May morning Guiteau was loitering outside of the White House when he spotted President Garfield strolling alone to church. Guiteau made secret chase. He found a vantage point outside a chapel window, but he was concerned for the safety of others and postponed the murder. Several days later Guiteau was among the onlookers as the president escorted his wife to the train station. Mrs Garfield was suffering from malaria, and she was being sent to the Jersey shore where the sea air was rumored to be reinvigorating. Guiteau did not wish to upset the ailing first lady, so he kept his pistol pocketed. The stalking continued on the evening of 01 June 1881 when Guiteau trailed the president and James Blaine through the shadowy streets of DC. The aspiring assassin was appalled to see the two men walking and talking arm-in-arm, but he lacked the nerve to act.
The opportunity to act came the next day, on June 2, 1881. Read what happened on that day, how Garfield's medical treatment contributed to his death, how Alexander Graham Bell figured in, and what happened to the delusional Guiteau, all at Damn Interesting. Link