Sen. Chris MurphyChristopher (Chris) Scott MurphyGOP online donor platform offering supporters 'Notorious A.C.B.' shirts Democratic senator calls for 'more flexible' medical supply chain to counter pandemics The Hill's 12:30 Report - Presented by Facebook - Don't expect a government check anytime soon 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) ManchinEnergy innovation bill can deliver jobs and climate progress The Hill's Morning Report - Sponsored by JobsOhio - Trump's tax return bombshell Sunday Shows: Trump's court pick dominates MORE (W.Va.), Patrick LeahyPatrick Joseph LeahyBipartisan representatives demand answers on expired surveillance programs Democrats shoot down talk of expanding Supreme Court Battle over timing complicates Democratic shutdown strategy MORE (Vt.), Al FrankenAlan (Al) Stuart FrankenGOP Senate candidate says Trump, Republicans will surprise in Minnesota Peterson faces fight of his career in deep-red Minnesota district Getting tight — the psychology of cancel culture MORE (Minn.), Cory Booker (N.J.), Bill NelsonClarence (Bill) William NelsonDemocrats sound alarm on possible election chaos Trump, facing trouble in Florida, goes all in NASA names DC headquarters after agency's first Black female engineer Mary W. Jackson MORE (Fla.), Dick DurbinRichard (Dick) Joseph DurbinHarris says she hasn't 'made a plan one way or another' on meeting Supreme Court nominee Trump, GOP aim to complete reshaping of federal judiciary The Hill's Morning Report - Sponsored by JobsOhio - Trump's tax return bombshell MORE (Ill.), Charles SchumerChuck SchumerDemocrats blast Trump after report reveals he avoided income taxes for 10 years: 'Disgusting' Biden refuses to say whether he would support expanding Supreme Court Schumer says Trump tweet shows court pick meant to kill off ObamaCare MORE (N.Y.), Ben CardinBenjamin (Ben) Louis CardinPelosi hopeful COVID-19 relief talks resume 'soon' Congress must finish work on popular conservation bill before time runs out PPP application window closes after coronavirus talks deadlock  MORE (Md.) and Ed MarkeyEdward (Ed) John MarkeyManchin opposes adding justices to the court A game theorist's advice to President Trump on filling the Supreme Court seat Watchdog confirms State Dept. canceled award for journalist who criticized Trump MORE (Mass.).

It also won support from presumptive Democatic presidential nominee Hillary ClintonHillary Diane Rodham ClintonOvernight Defense: Government funding bill butts up against deadline | Pentagon reports eighth military COVID-19 death | Trump, Pentagon collide over anti-diversity training push Voters split on whether Trump, Biden will win first debate: poll New Monmouth poll finds Biden with 6-point lead MORE and her rival, Sen. Bernie SandersBernie SandersPresident Trump faces Herculean task in first debate The Hill's Morning Report - Sponsored by JobsOhio - Trump's tax return bombshell New Biden campaign ad jabs at Trump's reported 0 income tax payments 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 McConnellTrump, GOP aim to complete reshaping of federal judiciary Supreme Court fight should drive Democrats and help Biden Harris on SCOTUS fight: Ginsburg's legacy 'at stake' 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 FeinsteinThe Hill's Morning Report - Sponsored by JobsOhio - Trump's tax return bombshell Hawley warns Schumer to steer clear of Catholic-based criticisms of Barrett Senate GOP set to vote on Trump's Supreme Court pick before election 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 CornynTrump, GOP aim to complete reshaping of federal judiciary Fears grow of chaotic election Supreme Court fight pushes Senate toward brink 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.