Senators dealt a devastating blow to gun control efforts Wednesday, defeating the background check compromise that was the centerpiece of President Obama’s post-Newtown push for stiffer laws and leaving advocates struggling to figure out what to do now.

The Senate also defeated efforts to ban some semi-automatic firearms and to limit the size of ammunition magazines. The series of votes showed that Congress remains bitterly divided between those who think the Second Amendment is paramount and those who say lawmakers must take any steps to prevent another school shooting.

Speaking about 90 minutes after the vote in the White House Rose Garden, an angry Mr. Obama called his opponents deliberate liars and said it was “a pretty shameful day for Washington.”

He urged voters to punish senators who voted to defeat expanded background checks.

“You’ve got to send the right people to Washington,” he said. “That requires strength and it requires persistence. I see this as just Round 1. Sooner or later, we are going to get this right. The memories of these children demand it.”

Mr. Obama doubled down on politics in other ways, blaming the defeat on the National Rifle Association and mocking arguments of opponents. At one point, he blurted out a rhetorical “Are they serious?” to the charge that he had been exploiting the shootings at Sandy Hook Elementary School in Newtown, Conn., by using its victims as props.

“The gun lobby and its allies willfully lied about the bill,” Mr. Obama said.

The president was surrounded by Newtown parents and former Rep. Gabby Giffords of Arizona, who was wounded in an assassination attempt. “It came down to politics,” he said.

The vote was the first major showdown since the December rampage, which left 20 schoolchildren and six faculty dead. The tragedy re-energized what had been a slumbering gun control movement.

They called for the semi-automatic and high-capacity magazine bans, but quickly realized that those were doomed to failure, so they shifted the weight of their efforts to try to expand background checks.

The background check amendment, sponsored by Sen. Joe Manchin III, West Virginia Democrat, and Sen. Patrick J. Toomey, Pennsylvania Republican, would have expanded instant checks to all Internet and gun show sales, but would have exempted in-person private sales. Law requires all sales by federally licensed dealers to undergo checks, regardless of how they are made.

The official tally on the Manchin-Toomey proposal was 54 votes in favor and 46 opposed — leaving backers six shy of the 60 needed for approval under the rules of debate.

The roll call would have been 55-45, but Senate Majority Leader Harry Reid, Nevada Democrat, supported the amendment but cast a “No” vote as a customary parliamentary maneuver, enabling him to demand a revote later. Of the 55 supporters, 51 were Democrats and four were Republicans. The opponents were four Democrats and 41 Republicans.

Opponents of the amendment said it would do nothing to stop gun violence, could infringe on the Second Amendment rights on law-abiding citizens and “would be a first step on the path to a national gun registry,” said Sen. Mike Johanns, Nebraska Republican.

Other Republicans said neither expanded background checks, nor the bans on magazines or semi-automatic weapons, would have prevented the Newtown shootings.

To underscore the weight of the issue, Vice President Joseph R. Biden presided over the vote, and families of gun-violence victims watched from the public viewing galleries.

“Shame on you,” a survivor of the 2011 Tucson shootings shouted at senators after the vote was announced.

Gun rights supporters did suffer losses, though. The Senate rejected an amendment to allow those with concealed-carry permits to carry their weapons across state lines.

Still, the background check amendment was the chief showdown.

Its defeat dooms what had become the “sweet spot” of gun legislation, as co-sponsor Sen. Charles E. Schumer, New York Democrat, described enhanced background checks, but creates significant logistical problems for broader gun measures.

Despite the setback, Mr. Reid said Democrats will try again.

“We have not given up,” he said. “I am going to do everything I can to fight for meaningful background check legislation.”

The underlying gun control bill Democrats wrote includes language intended to crack down on gun trafficking and straw purchases, as well as funding for school safety provisions. But it also includes even stiffer background checks, written by Mr. Schumer.

The Manchin-Toomey amendment was designed to replace the Schumer language, but now that chance is gone and the entire bill is threatened.

The Senate is scheduled to consider two amendments to the underlying bill Thursday. One would penalize states and local governments that release certain information about gun owners and victims of domestic violence, and the other would reauthorize and bolster programs on mental health and substance abuse disorders.

In 2004, the last time the Senate debated a major gun bill, the same situation occurred. Republicans wrote a bill to shield manufacturers from liability for gun crimes, but Democrats managed to attach amendments banning some semi-automatic weapons.

Neither side could stomach the final product, and 90 senators voted to kill it.

• Dave Boyer contributed to this report.

Sign up for Daily Newsletters Manage Newsletters

Copyright © 2020 The Washington Times, LLC. Click here for reprint permission.