Sen. Chris MurphyChristopher (Chris) Scott MurphyKerry responds to Trump accusation he violated Logan Act: 'Another presidential lie' Overnight Health Care: Senate panel to hold hearing on US coronavirus response | Dems demand Trump withdraw religious provider rule | Trump Medicaid proposal sparks bipartisan backlash Democratic senators urge Trump administration to request emergency funding for coronavirus response 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) ManchinLawmakers push back at Trump's Pentagon funding grab for wall Overnight Health Care: Appeals court strikes down Medicaid work requirements | Pelosi's staff huddles with aides on surprise billing | Senate Dems pressure Trump to drop ObamaCare lawsuit Senate Democrats pressure Trump to drop ObamaCare lawsuit MORE (W.Va.), Patrick LeahyPatrick Joseph LeahyDemocratic senators ask DOJ watchdog to expand Giuliani probe Overnight Defense: Senate votes to rein in Trump war powers on Iran | Pentagon shifting .8B to border wall | US, Taliban negotiate seven-day 'reduction in violence' Pentagon transferring .8 billion to border wall MORE (Vt.), Al FrankenAlan (Al) Stuart FrankenAl Franken blasts Susan Collins: She'll let Trump 'get away with anything' Bill Press: Don't forget about Amy Key moments in the 2020 Democratic presidential race so far MORE (Minn.), Cory Booker (N.J.), Bill NelsonClarence (Bill) William NelsonThe most expensive congressional races of the last decade Lobbying world Bottom Line MORE (Fla.), Dick DurbinRichard (Dick) Joseph DurbinDemocratic senators ask DOJ watchdog to expand Giuliani probe Trump commutes sentence of ex-Illinois Gov. Blagojevich in rash of clemency orders The Hill's Morning Report — AG Barr, GOP senators try to rein Trump in MORE (Ill.), Charles SchumerCharles (Chuck) Ellis SchumerDemocratic senators urge Trump administration to request emergency funding for coronavirus response Barr to testify before House Judiciary panel Graham won't call Barr to testify over Roger Stone sentencing recommendation MORE (N.Y.), Ben CardinBenjamin (Ben) Louis CardinDemocrats worried about Trump's growing strength Senate Democrats queasy over Sanders as nominee Schumer: Trump address 'demagogic, undignified, highly partisan' MORE (Md.) and Ed MarkeyEdward (Ed) John MarkeyKennedy, Markey spar over experience in first Senate primary debate The Hill's Campaign Report: Bloomberg to face off with rivals at Nevada debate Massachusetts Democrats question deployment of Border Patrol teams to sanctuary cities MORE (Mass.).

It also won support from presumptive Democatic presidential nominee Hillary ClintonHillary Diane Rodham Clinton'Where's your spoon?' What we didn't learn in the latest debate The Hill's 12:30 Report: Roger Stone gets over three years in prison; Brutal night for Bloomberg Poll: Democrats trail Trump in Wisconsin, lead in Michigan and Pennsylvania MORE and her rival, Sen. Bernie SandersBernie SandersNevada Democratic debate draws record-breaking 19.7 million viewers 'Where's your spoon?' What we didn't learn in the latest debate Ocasio-Cortez defends Warren against 'misogynist trope' 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 McConnellEverytown plans ad blitz on anniversary of House background check bill Kentucky state official says foreign adversaries 'routinely' scan election systems Don't let 'welfare for all' advocates derail administration's food stamp program reforms 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 FeinsteinCalifornia lawmakers mark Day of Remembrance for Japanese internment Democratic senators ask DOJ watchdog to expand Giuliani probe House passes bipartisan bill to create women's history museum 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 Medicaid proposal sparks bipartisan warnings Senate braces for fight over impeachment whistleblower testimony Booker, Cornyn introduce bill to fund school nutrition programs 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.