James Comey warned about "damage" to the US in the wake of President Trump's tweets.

Hours after President Trump tweeted about a "major spy scandal," former FBI director James Comey warned on Wednesday that the attacks against the FBI could cause "lasting damage."
"Facts matter. The FBI's use of Confidential Human Sources (the actual term) is tightly regulated and essential to protecting the country," Comey wrote on Twitter. "Attacks on the FBI and lying about its work will do lasting damage to our country. How will Republicans explain this to their grandchildren?"
In the recent past, Trump has posted numerous tweets concerning reports that an FBI informant interacted with some Trump campaign advisers.
"Look how things have turned around on the Criminal Deep State. They go after Phony Collusion with Russia, a made up Scam, and end up getting caught in a major SPY scandal the likes of which this country may never have seen before! What goes around, comes around!" Trump tweeted Wednesday morning.
A New York Times piece on Friday rebutted Trump's assertion of politically motivated spying, stating, "F.B.I. agents sent an informant to talk to two campaign advisers only after they received evidence that the pair had suspicious contacts linked to Russia during the campaign." 
However, the president has continued to echo his claim in delivered remarks and tweets.
"A lot of people are saying they had spies in my campaign," Trump told reporters on Tuesday. "If they had spies in my campaign, that would be a disgrace to this country.  That would be one of the biggest insults that anyone has ever seen, and it would be very illegal, aside from everything else.  It would make, probably, every political event ever look like small potatoes."