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 terrorists, and yet we have no scrutiny of the people on the terrorist watch list to be able to buy a gun?"
Analysis - Anthony Zurcher, BBC News, Washington
Monday night's vote on stricter gun regulation was a textbook illustration of modern political dysfunction in the US Congress.
With the public firmly supporting legislative action, both sides of the partisan divide came up with their own bills, both sides largely voted only for their proposals, and in the end nothing was accomplished.
Republicans accused Democrats of giving the government the power to arbitrarily prevent Americans from exercising their constitutional right to own a firearm based on a secretive "terrorist watch list" with no judicial oversight. Democrats charged Republicans with being more concerned with the support of the National Rifle Association than preventing the next gun-related massacre.
There is still the possibility of further Senate action - Susan Collins, a moderate Republican from Maine, is attempting to craft a bipartisan compromise.
But even if the Senate were to act, there are no indications that the House of Representatives - which contains conservative politicians more at risk of being unseated by a primary challenge from their right than a general election defeat - would even take a vote on such a bill.
Unless this dynamic changes, and politicians begin to fear consequences at the November ballot box, the gun-regulation deadlock is likely to endure.
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 at the time.
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
US newspaper reaction
"A week after Orlando, Republicans protect terrorists' right to bear arms" says the Dana Milbank in the Washington Post. He calls it an "absurd situation" where Republican senators put the US Constitution's Second Amendment above national security concerns. He says "Monday night was the best chance yet to block would-be terrorists from getting guns, and, as before, the Republican majority chose not to act."
The New York Daily News featured a mocked-up image of a blood-soaked Capitol building. "The only thing that's changed is the body count," wrote Cameron Joseph. "It felt like Groundhog Day on Capitol Hill."
USA Today called the vote "an extraordinary act of cowardice". The newspaper's editorial wrote: "These spineless lawmakers voted against advancing a commonsense measure. "Monday's votes showed, once again, that too many members are too cowed by the gun lobby to take the actions necessary to save lives."
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 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 agreed 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 had 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.