Sen. Chris MurphyChristopher (Chris) Scott MurphyGOP lawmaker demands ‘immediate recall’ of acting US ambassador to Saudi Arabia Dem senator calls for US action after 'preposterous' Saudi explanation Saudi mystery drives wedge between Trump, GOP MORE (D-Conn.) and other Democrats have taken over the Senate floor to call for tougher gun control laws and specifically action on keeping people on terrorist watchlists from buying firearms.

“I'm prepared to stand on this floor and talk about the need for this body to come together on keeping terrorists away from getting guns ... for, frankly, as long as I can, because I know that we can come together on this issue,” Murphy said in beginning the filibuster on Wednesday.

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Murphy began speaking at about 11:20 a.m., and the filibuster was still going more than 12 hours later.

Other Democrats who joined him included Sens. Richard Blumenthal (Conn.), Joe ManchinJoseph (Joe) ManchinElection Countdown: Takeaways from heated Florida governor's debate | DNC chief pushes back on 'blue wave' talk | Manchin faces progressive backlash | Trump heads to Houston rally | Obama in Las Vegas | Signs of huge midterm turnout The Hill's Morning Report — Presented by PhRMA — Early ballots pouring in with 15 days to the midterms Manchin wrestles with progressive backlash in West Virginia MORE (W.Va.), Patrick LeahyPatrick Joseph LeahyCongress raises pressure on Saudi Arabia Quote from Ford’s testimony spray-painted on Yale Law School entrance Corker: US must determine responsibility in Saudi journalist's death MORE (Vt.), Al FrankenAlan (Al) Stuart FrankenElection Countdown: Takeaways from heated Florida governor's debate | DNC chief pushes back on 'blue wave' talk | Manchin faces progressive backlash | Trump heads to Houston rally | Obama in Las Vegas | Signs of huge midterm turnout Dem holds single-digit lead in race to replace Franken GOP lawmaker once belittled sexual harassment: 'How traumatizing was it?' MORE (Minn.), Cory Booker (N.J.), Bill NelsonClarence (Bill) William NelsonElection Countdown: Takeaways from heated Florida governor's debate | DNC chief pushes back on 'blue wave' talk | Manchin faces progressive backlash | Trump heads to Houston rally | Obama in Las Vegas | Signs of huge midterm turnout Poll: Nelson leads Scott by 6 points in Florida Senate race Poll: Nelson tied with Scott in Florida Senate race MORE (Fla.), Dick DurbinRichard (Dick) Joseph DurbinFarm bill negotiators should take advantage of the moment The Hill's 12:30 Report — Trump says he is cutting foreign aid over caravan | Lawmakers point fingers at Saudi crown prince | DNC chair downplays 'blue wave' talk The Hill's Morning Report — Presented by PhRMA — Early ballots pouring in with 15 days to the midterms MORE (Ill.), Charles SchumerCharles (Chuck) Ellis SchumerManchin wrestles with progressive backlash in West Virginia The Hill's Morning Report — Presented by the Coalition for Affordable Prescription Drugs — Health care a top policy message in fall campaigns McConnell says deficits 'not a Republican problem' MORE (N.Y.), Ben CardinBenjamin (Ben) Louis CardinGOP leaders hesitant to challenge Trump on Saudi Arabia Dem senator: Trump accepts Saudi denials because he is 'enamored' with dictators Saudi mystery drives wedge between Trump, GOP MORE (Md.) and Ed MarkeyEdward (Ed) John MarkeyElection Countdown: O'Rourke goes on the attack | Takeaways from fiery second Texas Senate debate | Heitkamp apologizes for ad misidentifying abuse victims | Trump Jr. to rally for Manchin challenger | Rick Scott leaves trail to deal with hurricane damage Senate Dems ask Trump to disclose financial ties to Saudi Arabia Dems damp down hopes for climate change agenda MORE (Mass.).

It also won support from presumptive Democatic presidential nominee Hillary ClintonHillary Diane Rodham ClintonHillicon Valley: Bolton tells Russians 2016 meddling had little effect | Facebook eyes major cyber firm | Saudi site gets hacked | Softbank in spotlight over Saudi money | YouTube fights EU 'meme ban' proposal Dems lower expectations for 'blue wave' Election Countdown: Takeaways from heated Florida governor's debate | DNC chief pushes back on 'blue wave' talk | Manchin faces progressive backlash | Trump heads to Houston rally | Obama in Las Vegas | Signs of huge midterm turnout MORE and her rival, Sen. Bernie SandersBernard (Bernie) SandersHarris presses young people to vote early in Iowa trip Dems lower expectations for 'blue wave' Election Countdown: Takeaways from heated Florida governor's debate | DNC chief pushes back on 'blue wave' talk | Manchin faces progressive backlash | Trump heads to Houston rally | Obama in Las Vegas | Signs of huge midterm turnout MORE (I-Vt.).

The Senate is currently considering an appropriations bill for the Commerce and Justice departments and science programs. Though no votes are currently scheduled, the senators are blocking any amendments to the bill.

"I don't think we should proceed with debate on amendments to this bill until we have figured out a way to come together," Murphy said, referring to the spending bill.

The Democrats are also technically blocking Majority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellElection Countdown: Takeaways from heated Florida governor's debate | DNC chief pushes back on 'blue wave' talk | Manchin faces progressive backlash | Trump heads to Houston rally | Obama in Las Vegas | Signs of huge midterm turnout Sanders: Democrats ‘absolutely’ have chance to win back rural America  Trump privately ready to blame Ryan and McConnell if Republicans lose midterms: report MORE (R-Ky.) from ending debate on the legislation, though a spokesman shot down any speculation that the Republican leader would have tried to wrap up work on the spending bill Wednesday.

Democrats have given no indication how long they plan to hold the Senate floor. Chris Harris, a spokesman for Murphy, said Democrats launched the talkathon because the senator will no longer accept “inaction or half measures in the face of continued slaughter.”

The effort comes three days after the deadliest mass shooting in U.S. history. A gunman armed with a Sig Sauer MCX rifle and a handgun on early Sunday killed 49 people at an Orlando nightclub. 

Murphy is well-known for his support for tougher gun control laws. One of America's most shocking gun crimes occurred in his home state in Newtown, where 20 children and six adults were shot to death at Sandy Hook Elementary School.

"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. 

Since the Orlando attack, Democrats have put a renewed focused on legislation meant to block the sale of guns to people on terrorist watchlists. 

An effort to move legislation was previously blocked last year. 

Sen. Ben Sasse (Neb.) was the first Republican senator to join Murphy and other Democrats, asking a question about the government's terror watchlists.

"I'm familiar with the terrorist screening database. There are a series of lists that fall from the database, but I don't think there's any such thing as 'the terrorist watchlist,' and I certainly don't understand what due process rights would apply," Sasse said.

Sasse's comment reflects a central problem Republicans have with a proposal from Sen. Dianne FeinsteinDianne Emiel FeinsteinPoll: Feinstein holds 18-point lead over challenger Durbin to Trump: ‘We’re the mob? Give me a break’ Sen. Walter Huddleston was a reminder that immigration used to be a bipartisan issue MORE (D-Calif.) that would give the attorney general broad authority to block people on watchlists from being able to buy guns or explosives. 

Republicans argue that could deny constitutional rights to Americans who aren’t actually tied to terrorism.

Instead, Sasse and most Republicans support an alternative proposal by Sen. John CornynJohn CornynManchin wrestles with progressive backlash in West Virginia O'Rourke's rise raises hopes for Texas Dems down ballot Five takeaways from Cruz, O'Rourke debate showdown MORE (R-Texas) that would allow the attorney general to delay suspected terrorists from getting a gun for up to 72 hours while seeking a court order to stop the sale.

Sen. Pat Toomey (R-Pa.), who faces a tough reelection bid, came to the Senate floor urging his colleagues to compromise. 
 
"There's an obvious opportunity here, guys, to work together and find the solution," he said. "What I'm suggesting is let's get to work here." 
 
Toomey on Wednesday criticized the Feinstein measure as "badly flawed." But he also said that Cornyn's proposal, which he previously voted for, likely didn't give enough leeway to the attorney general. 
 
He made the comments after Democratic Senate candidate Katie McGinty, who is hoping to unseat Toomey, pressured the GOP senator to back the Feinstein legislation during a press conference Tuesday. 
 
Wednesday afternoon, Toomey said he planned to introduce a compromise bill Thursday aimed at combining aspects of both the Feinstein and Cornyn proposals.
 
Toomey's legislation would require the attorney general to create a list of "likely terrorists" that could be blocked from buying guns. The list would then be submitted to the Foreign Intelligence Surveillance Court, which would review it annually and remove any Americans inadvertently included, according to a summary of the forthcoming bill from his office.

Updated at 11:35 p.m.