"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.
"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.
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"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".
terrorists have repeatedly called on supporters to attack Americans here at home.
"This act of terrorism is an attack on our freedoms. Our country must have the resolve to defeat ISIS. As a country, we need to do whatever it takes to destroy ISIS using whatever means possible to protect Americans at home and abroad," Boozman said.
Senator Jack Reed said while investigators are still gathering all the facts, the shooter was clearly a hate-filled individual.
Indian-American Congressman Ami Bera said this terrible crime is an attack on the core value of equality for all.
"The Senate's inaction on commonsense gun violence prevention makes it complicit in this public health crisis. Prayers and platitudes are insufficient," said Senator Richard Blumenthal.
"We must do everything in our power to stamp out these cowardice acts of terrorism and we must not feed the negative energies of hate and intolerance," said Congressman Tim Ryan.
It is absolutely infuriating to read reports that this shooter used an assault weapon to murder 50 innocent people and wound 53 more, said Congressman David N Cicilline.
"It just should not be this easy for someone to walk into a gun store and walk out armed with a weapon of war that is designed to kill as many people as quickly as possible," he said.
Congresswoman Kathy Castor said this horrendous circumstances remind that the Congress can act to reinstate the military, high-capacity assault weapons ban and pass legislation to prohibit any person on the national terrorism watch list from being able to purchase a firearm.