The US Senate has rejected plans to tighten gun controls, including the restriction of weapons sales to people on terrorism watch lists.
Four proposals were brought before the Senate after 49 people died in an attack on a gay nightclub in Florida.
But Democratic and Republican senators voted along party lines, blocking each other's bills.
Senators strongly disagreed about how to prevent more attacks happening in future.
Republican Senator John Cornyn said: "Our colleagues want to make this about gun control when what we should be making this about is the fight to eliminate the Islamic extremism that is the root cause for what happened in Orlando. My colleagues in many ways want to treat the symptoms without fighting the disease."
For her part, Democratic Senator Barbara Mikulski said: "Why is it we would go through such incredible scrutiny to board an airplane to protect me against terrorist, and yet we have no scrutiny of the people on the terrorist watch list to be able to buy a gun?"
Right to bear arms
Republicans and members of the National Rifle Association (NRA) complained that the bills put forward by the Democrats violated the constitutional right to bear arms. They are concerned that without enough "due process", law-abiding Americans wrongly named on watch lists would be prevented from buying weapons.
Democrats said the Republican proposals were too weak.
Eight days before the Senate's vote on Monday, Omar Mateen shot 49 people dead and injured many more in the worst mass shooting in recent US history.
Mateen was a US citizen who had been known to the FBI since 2013 but was not on a terrorism watch list.
In the US, gun dealers are licensed by the federal government. People can be prevented from buying weapons if they have mental health problems or are guilty of serious crimes, but there is no specific prohibition for those on the terrorism watch list.
There are currently about one million people on that list.
There are other ways to buy guns — at gun shows, or from a private vendor online — that do not require any background checks.
The Senate voted down legislation that would have closed a gun show loophole and expanded background checks to cover private sales.
Also rejected were
A bill to ban suspects on terrorism watch lists from buying guns
A bill (backed by the NRA) that would allow the US attorney general to delay a gun purchase by a known or suspected terrorist, but prosecutors would need to convince a judge of the would-be-buyer's connection to terrorism within three days
A bill that would alert the FBI to terrorism suspects who have purchased a gun, without blocking the purchase outright
Filibuster
Last week one Democrat took the House floor for nearly 15 hours to demand action on gun control, after the attack on Pulse nightclub in Orlando.
Connecticut Senator Chris Murphy, a Democrat, held the floor on Wednesday night in a "filibuster," a tactic that enables lawmakers to block proceedings.
The filibuster came to an end when Republicans eventually pledged to hold votes on measures for expanding background checks and preventing people on terrorism watch lists from obtaining guns.
After Monday's vote, Mr Murphy said the Senate's inaction compounded the suffering of victims of gun violence.
He said: "I believe that for all of the scarring psychological harm that comes with losing a loved one or a neighbour, more harm is piled on when you find out that the people that you elected to run your country just don't care. It hurts something awful when you lose someone, but it gets worse when your leaders are silent, are totally silent, in the face of your personal horror."
Though partisan differences plague debate in the Republican-dominated chamber, the bills reflect a shift in American sentiment on guns.
Senator Susan Collins from Maine is working with fellow Republican Senator Kelly Ayotte on a compromise bill to prohibit the sale of guns to terrorism suspects on the no-fly list, and to create an appeals process for people who might be on the list by mistake.