Donald Trump isn't pausing his political commentary for the biggest mass shooting in U.S. history unfolding in Florida.

It was unclear whether the shooter who killed at least 50 people in an Orlando, Florida nightclub was associated with a radical religious organization. President Barack Obama addressed the nation, calling the shooting "an act of terror" and an "act of hate."

Trump tweeted as Obama began speaking: "Is President Obama going to finally mention the words radical Islamic terrorism? If he doesn't he should immediately resign in disgrace!"

A law enforcement official tells The Associated Press that the shooter was known to the FBI before the incident. The official was not authorized to discuss the ongoing investigation and spoke on condition of anonymity.

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