Sen. Chris MurphyChristopher (Chris) Scott MurphyMurphy criticizes anti-abortion lawmakers following Michigan school shooting Republicans struggle to save funding for Trump's border wall Senate Democrats call on Biden to push for COVID-19 vaccine patent waivers at WTO 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 ManchinJoe ManchinOvernight Energy & Environment — Presented by ExxonMobil — Manchin seeks 'adjustments' to spending plan Pence-linked group launches 0K ad campaign in West Virginia praising Manchin Democrats push tax credits to bolster clean energy MORE (W.Va.), Patrick LeahyPatrick Joseph LeahyBiden signs four bills aimed at helping veterans The Hill's Morning Report - Ins and outs: Powell renominated at Fed, Parnell drops Senate bid On The Money — Biden sticks with Powell despite pressure MORE (Vt.), Al FrankenAlan (Al) Stuart FrankenFranken rules out challenge against Gillibrand for Senate seat Franken targets senators from both parties in new comedy tour Al Franken on another Senate run: 'I'm keeping my options open' MORE (Minn.), Cory Booker (N.J.), Bill NelsonClarence (Bill) William NelsonNASA spacewalk delayed due to debris threat This Thanksgiving, skip the political food fights and talk UFOs instead Two trajectories to Mars by the 2030s MORE (Fla.), Dick DurbinDick DurbinManchin working on 'adjustments' to energy policies in Biden spending plan Schumer: 'Good conversation' with McConnell on debt hike  Graham emerges as go-to ally for Biden's judicial picks MORE (Ill.), Charles SchumerChuck SchumerThe Hill's Morning Report - Presented by Facebook - The omicron threat and Biden's plan to beat it Lawmakers take aim at 'Grinches' using bots to target consumers during holidays Democratic frustration growing over stagnating voting rights bills MORE (N.Y.), Ben CardinBenjamin (Ben) Louis CardinIt's time for Congress to guarantee Medigap Health Insurance for vulnerable Americans with kidney disease Senators call for Smithsonian Latino, women's museums to be built on National Mall Democrats plow ahead as Manchin yo-yos MORE (Md.) and Ed MarkeyEd MarkeySenators seek to curb counterfeit toys and goods sold online Senate GOP blocks defense bill, throwing it into limbo Equilibrium/Sustainability — Presented by Southern Company — Pledged money not going to Indigenous causes MORE (Mass.).

It also won support from presumptive Democatic presidential nominee Hillary ClintonHillary Diane Rodham ClintonCountering the ongoing Republican delusion Republicans seem set to win the midterms — unless they defeat themselves Poll: Democracy is under attack, and more violence may be the future MORE and her rival, Sen. Bernie SandersBernie SandersOn The Money — Powell pivots as inflation rises Pence-linked group launches 0K ad campaign in West Virginia praising Manchin Senators huddle on path forward for SALT deduction in spending bill 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 McConnellSenate nearing deal on defense bill after setback On The Money — Powell pivots as inflation rises Schumer eyeing Build Back Better vote as soon as week of Dec. 13 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 FeinsteinNew variant raises questions about air travel mandates Progressive groups urge Feinstein to back filibuster carve out for voting rights or resign Senators call for Smithsonian Latino, women's museums to be built on National Mall 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 CornynCongress's goal in December: Avoid shutdown and default Mental health: The power of connecting requires the power of investing Senators call for Smithsonian Latino, women's museums to be built on National Mall 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.