"Confronting the threat of violent homegrown radicalisation is one of the greatest counterterrorism challenges our law enforcement and intelligence community faces," Florida Senator Marco Rubio said.
"We are a nation at war with Islamist terrorists. Theirs is a repressive, hateful ideology that respects no borders. It is a threat to our people at home and abroad," House Speaker Paul Ryan said.

Congressman Robert C 'Bobby' Scott, a vice chair of the House Democratic Caucus' Gun Violence Prevention Task Force and member of the Congressional LGBT Equality Caucus called for a strong gun control laws.
"These tragedies are far too common and we cannot continue to sit idly by as these incidences continue to happen. Congress must review every available proposal to determine what we can do to reduce all forms of gun violence.
"Americans are understandably frustrated at our inability to come together to address this problem in a meaningful way. I will continue to fight for evidence - based policy proposals to address this issue. I just hope that the leadership in Congress will finally agree that enough is enough. Meaningful action is long overdue," Scott said.
Senator Tom Carper, top Democrat on the Homeland Security and Governmental Affairs Committee said this horrific attack reminds that the US must remain vigilant at home against threats of terrorism.
"It is critical that federal, state and local law enforcement officials work together to get to the bottom of this attack," he said.
"As we learn more information about this tragedy, we must remain steadfast in our commitment as a nation to acknowledge the threats we face and do everything we can to root out terror," Senator John McCain said.
Member of the Senate Select Committee on Intelligence Senator Susan Collins described this as worst attack on the US since 9/11 and the worst mass shooting in "our history".
"If the FBI's investigation confirms allegations that the attacker pledged his allegiance to ISIS or if he proves to have been a lone wolf, this attack is yet another stark reminder that the US is not immune from the threat of violent extremism," she said.

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