More than a week after ISIS supporter Omar Mateen opened fire at an Orlando nightclub, leaving 49 dead and 53 wounded, congressional Democrats have dramatically ramped up the rhetoric against Republicans over gun control, accusing the GOP of arming Islamic terror groups.

A week after Connecticut Senator Chris Murphy conducted a 15-hour speaking filibuster, House Democrats shut-down the chamber with a “sit-in” protest, demanding increased restrictions on gun ownership.

When the chamber shut down and the live C-SPAN feed halted, legislators used cellular phones to stream the sit-in over the internet.

On Monday, Murphy launched a scathing attack on Republicans, accusing them of arming the ISIS terror organization and holding the GOP responsible for the Orlando massacre.

“We’ve got to make this clear, constant case that Republicans have decided to sell weapons to ISIS,” Murphy told the Washington Post. “That’s what they’ve decided to do.”

“We’ve got to make this connection and make it in very stark terms.”

The comments came hours before four gun control bills came up for a vote in the Senate – two proposed by Democrats, two by Republicans. All four failed to pass the 60 vote threshold needed to avoid a filibuster.

On Tuesday Massachusetts Senator Elizabeth Warren expressed support for Murphy’s comments, tweeting “@ChrisMurphyCT said it right: “The @SenateGOP have decided to sell weapons to ISIS.”

Congressional Democrats have demanded tougher background checks and a comprehensive ban on gun purchases by individuals flagged on the kind of terrorist watch lists which prevent travelers from boarding flights – what is often referred to as a “no-fly” list.

But gun rights advocates note that the terrorist responsible for the Orlando massacre was a licensed security guard who had passed more comprehensive background checks than those proposed in the wake of the attack.

And applying the no-fly list rules to gun purchases, critics say, would violate due process, adding that people are frequently placed on the list by mistake. Democratic congressman John Lewis, for instance, who participated in Wednesday’s sit-down protest, was accidently included on the no-fly list.