Democratic Sen. Chris Murphy of Connecticut took the Senate floor Wednesday morning calling for a vote over a proposal to prevent people on the FBI’s terrorist watch list from buying firearms.

He wouldn’t relinquish it for close to 15 hours.

After 2 am Thursday, when Murphy hadn’t sat down or used the bathroom since the filibuster began, he ended the speech with a declaration of victory: The Senate will vote on two gun control measures. One would bar those on federal terror watch lists from obtaining firearms, and the other would mandate background checks for purchases at gun shows and over the internet.

I am proud to announce that after 14+ hours on the floor, we will have a vote on closing the terror gap & universal background checks — Chris Murphy (@ChrisMurphyCT) June 16, 2016

Throughout Wednesday, Murphy’s filibuster looked mostly like an expression of frustration over congressional inaction on mass shootings. But the filibuster accomplished its goal of drawing public attention to congressional inaction on gun control, even on modest measures supported by the majority of Americans.

What are the measures that Sen. Murphy is calling for a vote on?

After news that Omar Mateen, who killed 49 people and injured 53 at the Pulse gay nightclub in Orlando on Sunday, had been investigated by the FBI in the past for possible terrorist ties, Senate Democrats began pushing for new measures to block suspected terrorists from buying guns.

The legislation, proposed by California Sen. Dianne Feinstein, would give the federal government the right to ban gun sales under a "reasonable suspicion" that the prospective buyer is participating in or funding a terrorist plot.

As they have in the past, Democrats framed the bill, as well as another proposal requiring background checks for gun buyers no matter where they purchase the weapon, as a commonsense measure for fighting terrorism that could only be opposed by those with absolutist opposition to gun control.

"People shouldn’t look at that as a partisan issue," said Oregon Sen. Ron Wyden. "Americans want to know why anybody would vote to allow individuals suspected of terrorist ties and motivations to purchase regulated firearms."

The measure is typical of the new Democratic approach to gun control. In the 1990s, Democrats focused on banning types of guns they thought were especially dangerous, such as military-style assault rifles and magazines that allow shooters to fire many rounds of ammunition without reloading.

But since the Sandy Hook shootings in 2012, they've focused instead on blocking "dangerous people" from purchasing weapons — people who are on the no-fly list, for example, or who have been diagnosed with a mental illness.

Blocking certain kinds of people from purchasing guns has more bipartisan support than banning types of guns that seem especially dangerous, as this Pew Research Center poll from last summer shows:

As President Barack Obama said two weeks before the shooting in Orlando: "We're allowed to put them on the no-fly lists when it comes to airlines, but because of the National Rifle Association, I cannot prohibit those people from buying a gun."

He continued: "This is somebody who is a known ISIL sympathizer, and if he wants to walk into a gun store or a gun show right now, and if he wants to buy as many weapons and ammo as he can nothing is prohibiting him from doing that."

Republicans — and some left-leaning civil liberties advocates — oppose these ideas

Republicans have opposed blocking people on no-fly lists or watch lists from buying guns, saying they worry that doing so would infringe on the rights of gun holders who may be wrongly included on the list.

On Wednesday, the Atlantic noted that the American Civil Liberties Union also opposes the initiative, in part because some people on those terrorist watch lists haven't necessarily been accused or convicted of a crime.

"We don't want terrorists to be able to walk into a gun store and buy a gun, but we don't want an innocent law-abiding citizen to be denied his Second Amendment rights because he's on a list with a bunch of terrorists," said Pennsylvania Sen. Pat Toomey, a Republican, in an interview with the Courant this week.

The idea doesn’t enjoy unanimous support in left-leaning circles, either: Slate’s Mark Joseph Stern, for instance, argues that it would create serious civil liberties risks, particularly over due process concerns, and Vox’s German Lopez has also outlined the liberal case against the idea.

"If the government can revoke your right to access firearms simply because it has decided to place you on a secret, notoriously inaccurate list, it could presumably restrict your other rights in a similar manner," Stern writes. "You could be forbidden from advocating for causes you believe in, or associating with like-minded activists; your right against intrusive, unreasonable searches could be suspended."

Why Murphy’s filibuster began and gathered steam

On Wednesday, Senate Democrats were trying to pass two gun control measures by adding them onto an unrelated spending bill funding the Commerce and Justice departments.

The Republican leadership was expected to move on with the spending bill without the gun amendments. To stall that from happening, Murphy launched the filibuster to block Senate Majority Leader Mitch McConnell from ending debate on the spending bill.

Murphy was responding to a specific instance — the failure of Congress to respond to the deadly Orlando attacks. But he stressed that his filibuster was a response to the much longer-running lack of congressional action in response to mass shootings.

The big problem, Murphy emphasized, was that Congress has consistently failed to act after attacks like the one in San Bernardino, California, last fall.

Murphy has called for stricter gun control measures since 20 young children in his state were killed at the Sandy Hook Elementary School in 2012 — an experience he spoke about in personal terms throughout the filibuster. (Murphy was elected one month before the killings at Sandy Hook.)

"I can’t tell you how hard it is to look into the eyes of the families of those little boys and girls who were killed in Sandy Hook, and tell them that — almost four years later — we’ve done nothing. Nothing at all," Murphy said.

Most of his fellow Democratic senators had no idea the filibuster was coming. But two of them — New Jersey’s Cory Booker and Connecticut’s Richard Blumenthal — quickly helped, asking questions to give Murphy a rest from talking without forcing him to yield the floor.

More and more Democratic senators stepped forward to ask questions. By 8:30 pm, more than 15 of them had spoken. By a little after 10 pm, 38 of 46 Democratic senators had joined the effort.

As they did, the story ricocheted around social media. Murphy, sounding surprised, said close to midnight that his office had received more than 10,000 phone calls since he began talking.

"Our phone lines in our office are ringing off the hook, as we speak," Murphy said, sounding more energized than he had for hours. "People around the country are demanding that we continue to stand as long as we can."

Watch: 18 charts that explain gun violence in America