"The system is rigged. General Petraeus got in trouble for far less. Very very unfair! As usual, bad judgement," Trump said in a tweet, a few hours after the FBI Director James Comey announced that the investigating agency has concluded its investigation into the Clinton's email scandal.
Comey said the FBI would not recommend to the Department of Justice on charging former Secretary of State, who is now the presidential candidate of the Democratic party.
The Speaker of the US House of Representatives Paul Ryan said the FBI announcement defies explanation.
"No one should be above the law. But based upon the director's own statement, it appears damage is being done to the rule of law. Declining to prosecute Secretary Clinton for recklessly mishandling and transmitting national security information will set a terrible precedent," Ryan said.
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"The findings of this investigation also make clear that Secretary Clinton misled the American people when she was confronted with her criminal actions. While we need more information about how the Bureau came to this recommendation, the American people will reject this troubling pattern of dishonesty and poor judgement," he said in a statement.
"Her actions were grossly negligent, damaged national security and put lives at risk," he alleged.
The Republican National Committee (RNC) Chairman Reince Priebus said the FBI's findings are a glaring indictment of Clinton's complete lack of judgement.
"We now know Clinton failed to turn over thousands of work-related records she certified were in the possession of the State Department, that more than one hundred emails contained material that was classified at the time they were sent or received, and that her server was less secure than Gmail and was likely hacked by hostile actors," he said.
Meanwhile, the Clinton campaign welcomed FBI's decision.
In a statement, Clinton's campaign spokesman Brian Fallon said: "We are pleased that the career officials handling this case have determined that no further action by the (Justice) Department is appropriate... We are glad that this matter is now resolved.