NBC News reports:
In the weeks after he became the Republican nominee on July 19, 2016, Donald Trump was warned that foreign adversaries, including Russia, would probably try to spy on and infiltrate his campaign, according to multiple government officials familiar with the matter.
The warning came in the form of a high-level counterintelligence briefing by senior FBI officials, the officials said. A similar briefing was given to Hillary Clinton, they added.
They said the briefings, which are commonly provided to presidential nominees, were designed to educate the candidates and their top aides about potential threats from foreign spies.